I count myself the luckiest and unluckiest woman in London. The luckiest because I have a great husband, a fabulous family with kids on track and growing up, a beautiful house, more friends than I deserve and as much interesting work as I want. This time a year ago, I'd put the dog on the lead and walk over to the local shops in the sunshine, marvelling at my own good fortune, thinking I wouldn't swap places with anyone in the world.

Then, at a stroke, this lovely run of luck ran out. On 26 November 2004, at the age of 'just' 49-and-a-half, which my kids think is ancient but seems pretty young to me, I discovered that the irritating, niggly cough I had had for the past two months was no trivial chest infection but an aggressive adenocarcinoma that had already spread well beyond the organ of origin - my lungs - to my bones, lymph nodes and possibly my liver as well. The irony of my situation was apparent to everyone who knew me. I was never ill, never down, a runner of half-marathons, and a yoga freak and nutrition nut to boot.

I knew how to look after myself big time. After all, it was my job. I had been writing about women's health for more than a quarter of a century, first as health editor of Vogue and then for a range of magazines and newspapers. I was the published author of not one but four books about preventive health. Since giving up smoking 23 years ago, I had joined the ranks of those fanatically intolerant antismoking ex-smokers. And yet here I now was, struck down by lung cancer, with its serves-you-right stigma.

Faced with the facts of my unenviable situation, it was hard not to feel incredulous. I looked like a well woman - and with the exception of the cough, and the recurrent one-sided headaches, and the pain in my left hip, and the three-quarters of a stone that had unaccountably tumbled off since September, I felt a well woman. How could I have a stage IV cancer that, even now, was racing round my body, invading my vital organs, threatening to kill me? And quite soon by all accounts. 'Don't look up your cancer on the internet,' my consultant warned me just before backing out of my side-room at University College Hospital. 'You'll only terrify yourself.'

I didn't, but even so, it didn't take long to find out that in the world of advanced cancer, stage IV is as bad as it gets. There is no stage V. It was the worst of all news - 'as bad as it can get', confirmed the nurse at the Middlesex Hospital who rang to inform me that the CT scan had revealed mets (metastases, or spread) in my liver. Was there anywhere that this cancer wasn't? And yet, though I was reeling from the discovery that few of my vital organs seemed to be free of this thing, I didn't feel my luck had entirely run out. Even then, I continued to count myself fortunate.

How so? Well, I had the highest level of support imaginable. I would look at my companions in the Middlesex chemo suite, alone and unsupported, undergoing their notoriously tough treatments and then having to find their own way home, and I felt extraordinarily blessed. I happen to be married to one of the most remarkable men on the planet - the kindest, funniest, most generous, emotionally intelligent human being in existence. We have four gorgeous and exceptionally warm-hearted children, Freddie, aged nine, Clemmie, 12, Romilly, 15, and Archie, 17. Fanning out from there, in both directions, we are lucky enough to have large, close-knit families, including in my case a twin sister, non-identical, who dropped everything immediately and raced up to be with me.

Add a world-class network of friends and neighbours, who were determined from the outset to save me so much as a second of unnecessary stress or strain, and Marvellous Maggie, the palliative care nurse who was allocated to me following my very first clinic appointment. From the outset, she has taken my welfare, physical and emotional, to heart, regularly ringing me, always prefacing her call with 'Is this a good time?', organising my pain relief, coming to see me and, in her calm, reassuring tones, answering all my questions as well as those of my children, whom she has also taken under her wing. Factor in all of this, and you will see that I was in the world's best possible position to receive the world's worst possible news.

Before the week was out, for example, a supper rota had been set up by one mover and shaker in our north London street, sparing me the hassle of thinking or planning or shopping or cooking for my family. Knowing how quickly the best intentions can dissolve in the face of the demands of a busy life - all these women, whom I have taken to calling the 'Colander Girls', have families to raise, and most have jobs, too - it amazes me that, six months on, they are still dishing up their delicacies and that more are requesting to join the rota every month. At the time of writing, they now number 18. Back then, the idea was inspired. If I was in shock, and quite unable to know what to do or where to turn, my friends and family were, too. 'Shocked', 'devastated', 'numb', 'disbelieving' - these were the adjectives that came up again and again in the avalanche of letters and cards arriving by every post, the flowers and gifts and phone calls we received at all hours of the day, every day. While this outpouring of love and concern was wonderfully uplifting, it was also bone-crushingly wearying. In fact, it soon became clear that if the cancer didn't finish me off sharpish, the telephone most certainly would. It rang and rang until we almost started hearing it in our sleep.

At the same time, I recognised that calls had to be taken and visits received. Friends and family needed the reassurance of seeing me and/or hearing my voice, still clear and strong, and to realise that, even though I was now under a sudden and most unexpected sentence of death, I was still very much with them. Most of all, they yearned to do something, anything, to help, to feel useful not useless, to support us in whatever way they could. 'It is not easy to work out how we who know you and love you, and who luckily do not have cancer as far as we know, can help,' wrote one close friend soon after the diagnosis. 'We know sometimes what to do. We know sometimes what not to do. Mostly we stumble around in the dark and try, crossing our fingers that whatever it is will prove right and not horribly wrong for you.'

As a person living with cancer, I would never presume to know what anyone else needs. I am just passing on aspects of my experience and that of the hundreds of others I have spoken to. The key, I quickly found, is to zero in on everyone's strengths and to build on them: ask the car drivers to take you places, the conscientious mothers to scoop up your children, the cordon bleu cooks to provide an evening meal, the good Christians (or Jews or Muslims or Buddhists) to pray for your healing and recovery. Ask friends whose intellect and judgment you respect to comb the internet for information on everything from cutting-edge new clinical trials to wacky-sounding alternative remedies, while screening out the unpalatable facts such as treatments and/or survival rates if they present more reality than you feel you can take.

Allow your good friends to act as gatekeepers of your diary, to keep visits at a manageable level, to field phone calls and to work out a rota of who will accompany you to hospital appointments, chemo or radiotherapy sessions, kidney or bone scans. Flowers and plants, lovely and cheering as they are, soon fade and die, and visits can be tiring, but help with the practicalities is an ongoing joy. The grim reality of cancer, and any other serious illness, is that life, with all its demands, continues: the children still need transporting to and from school, the dog needs walking, the laundry needs ironing and the daily meals need planning, preparing and dishing up.

These everyday tasks can feel overwhelming when you are feeling shell-shocked and are trying to fit them around the myriad visits to clinics and specialists that follow in the wake of every cancer diagnosis. 'What can I do to help?' you ask. Well, stand by, because the answer is: plenty.

Immediatley after the diagnosis people respond to the news that they have a life-threatening disease in all sorts of - often unpredictable - ways. The most panic-prone can become preternaturally calm, rising to the occasion in a way that can leave their friends stunned and even awestruck, while the steady, sensible types may temporarily whirl off-balance.

Leave your preconceptions at home. Accept us as you find us, and as the people we always were: requiring no special pitying voices, no different treatment, no deep, meaningful looks and embraces. Continue to argue with us about politics and football. Hug us if you always have. Otherwise, respect your distance.

Treat us as normally as you can and the odds are you'll soon find any distance and awkwardness dissolving. 'It was wonderful to see you, particularly as you are so much your old self,' emailed one friend a couple of months after my diagnosis, after we'd met for lunch. 'Somehow I'd imagined you horribly altered, and so it was reassuring to see you still feisty and funny and full of life.'

'I knew someone with cancer and I treated them normally. They liked that because everyone else treated them like they were ill all the time.' Jade Goody

'In an odd sort of way, I think one must let instinct take over. Go with the flow. It's about getting the balance right between "Life goes on" and "I'm here more than ever for you." It's about offering without intruding. It's about milestones, fixing holidays together six months ahead, helping to build confidence and yet not suddenly coming up with grandiose plans that you would never have made if things had been "normal". Yet things are normal. We are still the friends, loved ones, neighbours we always were. It's just that we are a bit more conscious of it than we used to be.' Jon Snow

'The thing is, people are different with me now and I want them to be normal. After we first heard about my mum, people kept coming up to me at school and saying, "How are you?" The teachers told the other girls I was having a hard time and then everyone came up to me, asking "What's happened to your mum?" and nagging me to tell them - that was very annoying.' Clemmie Stebbings, Deborah's daughter, 12

Offers of help can be like an answer to a prayer or they can be intrusive and unwanted. Bombarded by so many sincere offers, it can be difficult to say, 'Thanks very much, but no,' especially when the offers are so well intentioned. If we find it hard to say 'no', a trusted friend who can say 'no' on our behalf is of infinite value. I gradually learnt that life now was both too short and too precious to be polite for the sake of it, to have to endure calls or visits that I knew would be draining. Over time, I developed a self-preservational inner steeliness.

'One of the luxuries of having cancer - and there aren't many - is the increased ruthlessness it allows you in dealing with people. If a bore or a sponger invites himself around to see you, you say no. If an invitation to a dull dinner party arrives, you turn it down. Conversely, if you need to see a real friend, then you ask for their company or invite yourself to their house, because there is no room for shyness any more.' Martyn Harris, 'This is not the time to die', The Spectator, 19 August 1995

'There were some people I wanted to see and others I didn't want around. There's a way of being sympathetic and supportive without saying "Isn't it terrible?" all the time. People who were practical and sensitive to how I was feeling, who just knew how to put the cup of tea in the right place, were great, but others made demands on my time and my attention and my energy I just couldn't cope with. They meant well, but I learnt to get tougher. I would never have predicted that this illness would teach me not to be so polite.' Dr Ann McPherson

'The tidal wave of love and affection for Deborah and all of us was an enormous support. Don't, however, be surprised if not all kind invitations to lunch and a drink "to talk about it" are taken up. Having broken the news to close friends and relatives, I soon learnt not to do a string of late evening calls, as these only became more and more downbeat, leaving both parties sunk in gloom. Instead, I would wait till an upbeat moment with the family - a boozy lunch with laughter - before bringing the next instalment of news. This way, those not immediately with her could be left with a positive conversation to dwell on before my next call. Remember, too, that all children react differently in these circumstances (for this reason, perhaps, our two older children later said they were grateful to have had the news broken to them individually, rather than as a group, which was how we had originally intended to do it), yet at the same time are trying to protect us, as parents, from their own fears for the future.' Charlie Stebbings, Deborah's husband

While there is no second-guessing what anyone will want and need from you (for some an embrace or hug can substitute for 1,000 words, while for others it can feel like a horrible infringement), I found a surprising consensus about what people found helpful, or otherwise. Here is a summary:

Helpful A good friend sitting on my bed and just being there to lessen the loneliness, when trying to absorb the hugeness of what I'd just been told. Beautiful flowers and plants that arrived in their own containers and didn't need decanting. Uplifting letters with 'No need to reply' at the bottom; gossipy emails ditto. Having a friend on hand to answer the phone and tell well-wishers what was going on, especially boring ones. Fielding people who called at the house and telling them when it was time to go. People who treated whatever they did, however huge, as no big deal, the easiest thing in the world, rather than a grand gesture demanding my undying gratitude.

Unhelpful People hanging round with long faces, feeling terrible and looking worse, and not knowing what to say or where to put themselves. Having to feed well-wishers and make endless cups of tea. Treating me like a hero/heroine. Making assumptions about how I was feeling. Being bombarded with questions and/or advice. Arriving on the doorstep unannounced. People who seemed to be enjoying the drama, or who were clearly using the situation as another piece of gossip. Having to submit to intrusive questions and close embraces from people I hardly knew. People who broke down and cried.

'After the initial shock of finding out that Mum had cancer, all I wanted to do was lock up that part of my life in a tiny box that only needed to be opened when really necessary. But it can't work like that when the phone is going every three minutes with people wondering how your mum is and her having to tell and retell her story. Emails were definitely the way forward.' Romilly Stebbings, Deborah's daughter, 15

What should I say? You may think that we live in a more open society, where everything and anything is up for discussion. Think again. The conversational strictures around cancer remain every bit as constraining as the Victorian embargo on sex.

'I've lost count of the relatives who have met me at the door and said, "Don't you ever mention the words 'cancer' or 'death' or 'dying' in this house, or you won't be coming again." It can make your work much more difficult.' Maggie Bisset, nurse consultant in palliative care

'As soon as my mother heard the word "cancer", she fully expected to keel over the very next week, but she lived another 17 years and ended up dying from a completely different condition.' Rabbi Julia Neuberger

'When my best friend John Merritt was diagnosed with leukaemia, the first time he told me, he told me straight out, and then laughed and said, "What a bummer, eh?" Something like that. He had already worked out that, having dealt with the big blow himself, it was up to him to try to soften the blow for family and friends. So he made light of it. Of course, nothing does soften the blow. But I went into "It'll be OK" mode, prattling on about doctors and how great the NHS is, and he could see I was upset and not wanting to show it, and I could see he was panicking but didn't want to show it.' Alastair Campbell

'At the moment, I'm regularly in and out of the Royal Marsden holding coffee mornings for the ladies with breast cancer for the thesis I'm writing for my psychology degree, and what comes across loud and clear from talking to them is that what very often causes most anxiety is not the cancer but the reactions of the people around them. As friends and family, we have to remember that this is a time when their needs absolutely must come first. We cannot inflict our own fears and anxieties on them. We have to give them space. It's not our emotional trip.' Ruby Wax

An interesting study took place in the United States in which a number of people were taught the simple techniques of good listening. Volunteer patients then came to see them to talk about their problems. The listeners in this study were not allowed to say or do anything at all. They just nodded and said 'I see' or 'Tell me more'. They weren't allowed to ask questions, or to say anything at all about the problems that the patients described. At the end of the hour, almost all of the patients thought they had got very good help and support - and some of them rang the 'therapists' to ask if they could see them again, and to thank them for the therapy. From the CancerBACUP leaflet 'Lost for Words'

'At first I had a problem with knowing when they wanted to talk about it - the operation, the chemotherapy, the endless, endless blood tests - and when they didn't. I tried desperately to find a balance between seeming not to care enough and appearing a little too interested, morbid even. But slowly you get to spot when your daily "Hello, how are you?" needs to be extended to "Hello, how ARE you?" You just get a feeling that today is the day they want to say more than just "I'm fine, thanks." There are no rules, you just sort of get to know. You have to.' Nigel Slater

Accept that comparative tales of other people with cancer are rarely helpful. With hundreds of different types of cancer, and many different stages, it is rarely helpful to talk about other cases, since they almost certainly concern people of completely different ages, with a completely different cancer, in completely different circumstances. Two people who seem to have the same kind of cancer affecting the same part of the body may have quite distinct types of the disease and require alternative approaches to treatment.

Awful experiences of cancer are usually not just irrelevant; they are seriously depressing. Tales that don't have happy endings, or are prefaced with some gloomy fact about someone with advanced cancer 'who's been given six months to live', do not help us count our blessings. They are much more likely to add to the gloom.

'For some reason, everyone talks about the people who didn't survive. I had two primary cancers, which was pretty unusual. And when I got the second one, people told me such terrible bad-news stories, they instigated fears that weren't there in the first place. I do remember with such gratitude one doctor saying to me, "Two primaries? That's nothing. I've seen a patient with six." Sam Taylor-Wood

But avoid false reassurances, which could be seen to make light of the cancer. No one, sick or well, wants to dwell on the worst possibilities - conversations and preoccupations that seem morbid and depressing are distressing. But the fact is that the fear accompanying cancer is real, and realistic, not an example of negative thinking that we can be jollied out of.

The prognoses may vary, but cancer is always a serious disease that brings with it disturbing intimations of mortality. Fears and forebodings should be acknowledged rather than denied with a glib reassurance or speedy change of subject. Please do your best to understand that we may feel the need to prepare for the worst, while also doing our utmost to secure the best possible outcome. When I was concerned about the possible spread of my cancer, I found few friends prepared even to entertain the thought, let alone acknowledge the reality of my fear, as though merely to articulate this negative development would be enough to bring it about. Talking about the possibility or probability, even (my consultant would have said) certainty, of impending death was equally difficult. This meant that I was unable to share the things preying most upon my mind, apart from with a few dear, unfrightened individuals.

'My three good friends and one favourite aunt who have developed breast cancer have taught me that the important thing is simply to be there for them. To try to be the person with whom they can express whatever they want or need without worrying about how it sounds; without feeling they have to be strong and brave or you will somehow think less of them. As a friend, I need to be able to hear all this, without communicating how terrible and awful I feel, and without assuming this is their definitive "take" on the disease. It's just what they feel today. There's no point in pretending. So many people with cancer feel they don't have the permission to be fearful or downcast, or sad, or even defeated. They worry that any "negativity" will frighten their friends away or concern their family or jeopardise their survival chances. They shouldn't have to worry about these things, to [have to] put a brave face on. They should be able to do what they need to do and say what they need to say. And the rest of us should be able to cope with it.' Cherie Blair

Survivorship as with all cliches, the current cancer favourite - 'cancer is a word not a sentence' - has an element of truth. Increasingly, people are surviving their cancer, living with it, in the way that people with diabetes or epilepsy live with their conditions.

Given the pace at which medical research is proceeding - not a month goes by without news of some radical new drug transforming survival hopes for someone - certain experts predict that by 2015 cancer will have become yet another survivable disease, a chronic condition that we will die with rather than from.

While we may not choose the 'S-word' in relation to ourselves, the concept of survivorship is a useful one in that it implies that this is an acquired skill requiring practice rather than simply a passage of time the other side of treatment. For most of us, learning to live with cancer, rather than somehow existing despite it, is a huge adjustment. We come out of the long dark treatment tunnel into a period of what the cancer doctors call 'watchful waiting', marked by increasingly infrequent clinic appointments, and scans and tests at longer and longer intervals. And in place of the light, joy and general jubilation we were led to expect, we often find yet more anxiety, yet more fear, yet more uncertainty. Even with the best prognosis in the world, surgery for cancer can never be as straightforward as having our tonsils out, although everybody around us may let out a deep sigh of relief, and unhelpfully assume that it's OK now, they can all go home; everyone and everything can return to normal.

'I was 10 years old when I broke my arm playing football and they found a tumour on the bone. It really wasn't a big deal. Children accept everything as normal. I'm the youngest of five, and suddenly I was getting plenty of attention. Every time I went to the hospital we'd go and have lunch and ice cream. Then I had my operation and I can remember that, afterwards, I felt stronger tempered. My sister had breast cancer - mastectomy, chemotherapy and all the horrors. Recently she had the all-clear. "How 'clear' do you feel?" I asked her. "How clear is 'all'?" "Well," she said, "I've been taken off the books because today it's clear, and last year, and the three years before that, but I never stop thinking maybe they've got it wrong."' Monty Don

There are many ways of using one's experiences of cancer - particularly the negative ones - in a positive way, especially now that, after centuries of invisibility, patients are suddenly becoming a sought-after commodity. Our opinions are canvassed and our views are listened to, and patient representatives have become key presences on hospital committees and steering groups. 'If I jumped up and down in an effort to get anything changed,' said one member of my medical team, a touch ruefully, 'it wouldn't be nearly as effective.'

In this new era of patient power, any of us can use our experiences of healthcare (good and bad) to help improve the provision of services both locally and across the UK - whether by taking on the local hospital authorities about the cost and availability of parking, or campaigning to reduce waiting times for chemo and radiotherapy treatment. Actively engaging with politicians and decision-makers to effect change that will benefit others can be very empowering.

Be thankful for the good that comes out of a crisis. Through everything - the good, the bad, the ugly and the unrelievedly awful - is the enduring bond of real friendship, forged in crisis and tested by often extreme circumstances. Whether the friend you have supported goes on to enjoy several more years or even decades of life and outlives everyone, or dies from their disease as so many still will, the experience will have left you in countless small but important ways the richer for it.

'It was a very long-running thing. Ten years, after all. People had their own lives to lead. They'd appear in a real crisis, send flowers and presents, and come and visit. But Georgie's best friend's family were unbelievable. They could have backed off from the friendship. We would have understood. If Georgie didn't survive, and we all knew from the beginning that she could die, it was going to be very traumatic for their own daughter. But they were there right up to the last day of her life. They were there when we turned off her life-support machine. They changed her and got her ready and put on her nightie. They were incredibly supportive, very kind. And the links continue. We have just celebrated Georgie's friend's 18th birthday. Having been through all of that together, there is an unbreakable bond between us.' Nicola Horlick

However well or distantly we know someone, when we hear they have been diagnosed with this most dreaded of all diseases, if we choose to roll up our sleeves and do whatever we can to lighten the load on their shoulders, we will take something of enduring value away with us, whatever the eventual outcome.

Befriending a person in need is a skill. Even the specialist cancer nurses say they never stop learning, that they get better at it over time, adapting their approach in the light of what they learn from each new patient. Hardly surprising, then, that we, too, are continually learning as we go along; that the lessons we learn from being with one person, whom we may at times feel we have failed, we can apply with the next. And with one in three of us destined to join the ever-lengthening cancer statistics, what's quite certain is that there will always be someone else out there who needs our support, someone else to help ...

· What Can I Do to Help? 75 Practical Ideas for Family and Friends from Cancer's Frontline, by Deborah Hutton, is published by Short Books on 14 July at £7.99. For every book sold, all of the author's royalties, amounting to at least 35p per copy, will be paid to Macmillan Cancer Relief (registered charity number 261017)