When Cathy Rentzenbrink was a teenager her life was thrown into turmoil when her life-force of a brother was knocked over by a car. Emergency brain surgery prevented his death. A 10-day coma was followed by eight years of unthinkable family nightmare as he lay in a persistent vegetative state (“ugly words for an ugly condition”). Eventually, after complex legal proceedings, he died, and they could finally grieve.

She wrote about that experience in her previous book, the harrowing but beautiful memoir The Last Act of Love. Here she has a different purpose. While making reference to that tragedy, the focus here is on advice, and ways to get through the crises that will come our way.

Rentzenbrink is “not a doctor, a therapist, a philosopher, a priest or an expert on anything”, but she certainly has known heartache. And in clear and warm fashion, Rentzenbrink has written a lovely, simple book about how to cope with life’s bumps and shocks and sadnesses. There is a lot of intelligence here – it brims with it – but it is presented in such an informal way that it always has the feel of someone sitting by your bedside, rather than standing behind a lectern.

Even when she talks about Stoic philosophy or Japanese ceramics she does so in a relaxed, everyday way, and fuses it with references to Harry Potter. She is comforted by Marcus Aurelius, the Roman emperor who wrote a series of meditations and reflections to keep himself on the straight and narrow. She finds it a comfort to discover that almost two millennia ago that great powerful emperor was “fretting about pretty much the same stuff as I do now. Of course, he didn’t have Twitter to navigate but I guess being emperor and having your face on all the coins leads to some fairly significant authenticity worries.” The therapy she gets from the emperor is his idea that we are small within the vast expanse of things, so make of it what you will, and keep that perspective.

Most of the reference points, though, are thoroughly human ones, like sitting in a doctor’s waiting room with depression, and feeling guilty that everyone else in the room looks like they need far more help than you do. In this chapter, on mental health, she says that what has helped her is thinking of her depression the way she would think of an injury, or acne: something that can be treated. “The mind is simply another part of the body. It works hard, deserves our care and we shouldn’t feel ashamed about needing to give it some attention.” All common sense, of course, but sense isn’t always that common, especially when in the throes of a crisis.

And this is why it is a major asset to this book that Rentzenbrink isn’t a doctor or a therapist. This is not an academic text. It may be chicken soup for the soul, but this isn’t a wiser-than-thou self-help book. One of her tips, as an avid book lover, is to read “gentle, comforting, funny things” and that is what she herself is offering here. Not just a comfort in the advice she offers, but in the reassuring way she is choosing to offer it. Very often Rentzenbrink is giving advice to herself, as much as to the reader, acknowledging that she as much as any of us is a work in progress.

The chapters, to make things as soothing as possible, are all quite short and easy to digest. My favourite was the one called “Instructions to My Future Self”. And of course, via talking informally to herself (“My dear, my dear”), she is also talking to us the reader. “Somewhere in the future you are in a bit of a pickle.” That’s going to be all of us, isn’t it, at some point? Pickles are universal. And the advice is straightforward, and works for most of us too. Beware of alcohol, caffeine and social media. Stop beating yourself up for things beyond your control. She also tells herself to write things down honestly, and as with The Last Act of Love we get the subtle feeling that the very process of writing this book was a kind of therapy. It comes from a place of bleakness, but turns into a tender appreciation of life’s beauty.

At one point she thinks of Nancy Mitford saying that though life is often dull and sometimes sad there are currants in the cake. “Look for the currants.” Ultimately, we might never fix our broken hearts, but we can still live, and our hearts can grow and appreciate life’s wonder. That is the feeling the reader is left with. It is fair to say Rentzenbrink has added another lovely currant to the cake.

• A Manual for Heartache by Cathy Rentzenbrink is published by Picador (£8.99). To order a copy for £7.50 go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99