It was spring time in New York, a time when love and sex should be in the air. We had a month left to complete the manuscript of our sex manual, The Big Bang. After a tense afternoon editing the cunnilingus chapter (culminating in an argument over whether or not 'muff-diving' was a funny euphemism), we decided to take two days off from each other and the book before the final stretch. That weekend, we each unexpectedly - and unknown to the other - broke up with our boyfriends.

They had been our more-than-willing research assistants for the previous six months, a particularly important role given that our writing schedule left time for nothing but sex and writing about it. They had forgone the niceties (and occasionally even the foreplay). Suddenly, with a chapter on intercourse positions still to go, we were without guinea pigs and too depressed to start interviewing replacements. In fact, all we were in the mood for was Shirley Valentine, pizza and a bottle of cheap red wine.

But not even sex writers get love-sick days. And so, in order to figure out how best to describe positions such as 'the Red Cross' and 'the Weave' to readers, we were forced to strike these poses with each other on Em's living room floor. Then we rented Shirley Valentine, ordered a pizza and got drunk.

This is the life of a sex writer - at least, this is our life. During phone interviews with shock-jock radio DJs, we like to joke that we're taking the call from our chaise longue, dressed in negligées, on the verge of a pillow fight... and they believe us. We have neither the budget nor the wardrobe space to be the real-life Carrie Bradshaws.

But please don't confuse us with that other mythical breed of sexual literati: the yoga enthusiast with a vast collection of massage oils and purple accessories. We're the kind who prefer karaoke and happy-hour Budweisers to $15 Cosmopolitans, who stay home to watch Pop Idol, who miss rent payments, who occasionally have bad sex... or no sex at all.

Don't get us wrong - we love our day job. We'll be writing together at a café somewhere when one of us will look up and ask: 'How did we get to do this for a living?' And then: 'Do we hyphenate blowjob?' Once we pack it in for the day and find a bar to unwind, we're never at a loss for icebreakers with strangers. Our career choice lets us be as saucy as we like and claim it's 'professional curiosity'; or we can be retiring and prudish and our fellow party guests (usually) find the juxtaposition mysterious and charming or better yet - we can be a bit of both.

Mostly, people seem to want to talk about our sex lives. Apparently, a detailed history of the last blowjob one of us administered is vital to their sexual edification - they claim it's the only way to determine if we're truly qualified to give advice (while we feel it's more like asking your tax adviser how much he pulled in last year). If we had a nickel for every time someone asked us: 'How do you do your research [wink, nudge, ooh-err]?', we wouldn't have to write about sex for a living.

While we want to be unabashed and unashamed about our own sex lives, we like to preserve a little privacy. We're shy, we still blush and we believe there is such a thing as oversharing. Em once met a young man at a bar. A mere 45 minutes into their acquaintance, he cornered her and asked if she would mind taking a look at his penis. 'I've always been a little insecure about my size and I thought you could tell me if I was below average.' As he started to whip it out, she made a dash for the bar. 'But wait,' he called after her, zipping up, 'I thought you were a professional!'

But what about when one of us makes it home with someone? That's when we wish we were accountants. While we're obviously slightly better informed than the average shagger, it doesn't guarantee a more confident bedside manner. Nobody expects an accountant to be amazing in bed every single time, to be able to anticipate her partner's every want and need, to be multi-orgasmic and free of all sexual and physical insecurities.

Em, the more prolific dater of the two of us, frequently feels the need to qualify her first encounters with a disclaimer to ward off any disappointment on her partner's part: 'Just because I wrote the book...' or: 'Lo wrote most of that chapter...' or: 'You know the adage about those who can't do...' Sure, he'll lay claim to some nerves of his own - about how he'll stack up or what she might write about him later (though the latter is largely wishful thinking or arrogance in disguise).

This kind of hesitation is only gentlemanly, after all, the kind of thing he might say before offering his crisps-and-tuna casserole to a professional chef, for example. But mostly, he's just wondering what kind of dish she'll be serving up. After all, if the encounter is disastrous, he'll always have a good story: 'I slept with a sex columnist and all I got was this lousy hand job.' As a pedagogue of the prurient arts, we never get to be the naughty librarian in the bedroom, because to play against type would be to have sex like, well, like a librarian.

Fear of being a cliché usually saves us from ourselves, fortunately. The psychiatrist who's an emotional wreck, the chubby personal trainer, the over-permed, over-dyed hairdresser... it's all so done. While it's certainly easier to dish out advice than it is to follow it, we have learned how to take our own medicine, even if that means occasionally recalling an eager reader's email suggestion (complete with unflattering, naked self-portrait) right before climaxing.

The only other downside to taking one's own sex advice is the possibility of a new partner recognising a patented manoeuvre. Thus, though we are shameless in our self-promotion and never pass up an opportunity to hawk our sex manual, we forbid potential partners to read The Big Bang. At least for the first few encounters.

This kind of book banning also prevents guys from wooing us with our own tips and tricks. There's a certain comfort level you need to attain before you can emotionally handle a guy quoting you back to yourself in the bedroom, and it goes way beyond the comfort level required to get naked together.

The trouble with writing on a topic that frequently requires a 'try it, you might like it!' approach is that there are some things people just expect you to dig. Cunnilingus, for one. Being a sex writer who doesn't go ga-ga for oral pleasure is apparently more controversial than being a movie critic who dismisses Fellini as a hack. Invariably, the guy in question thinks you're just making excuses to avoid hurting his feelings about his poor technical skills. You feel an occupational responsibility to reassure him.

And thus, all too often you end up lying back and taking one for the team. (We know: rough life.) Because when a guy hears a sex writer say: 'Oh yeah, I like it like that' or: 'Ouch, not quite there', he assumes you're speaking for the masses, no matter how many times you remind him that your instructions are simply what gets you off. Today. In this position.

And then, of course, there are the things you think you have an obligation to have tried: bacchanalian orgies, sex slings suspended from the ceiling, flagellation with a riding crop, dressing up in a crotchless bunny suit. Odd, the things that can make you feel like a fraud in this business.

There are some sex writers who refuse to write about anything they haven't tried. This is not an approach we take. We're quite comfortable with our taboos. That's why we have loose-lipped friends whose taboos don't overlap with ours. That's why we interview 'experts' in each field and enlist doctors to help us with the science side of things. That's why we turn to that bottomless pit of sexual extremists, the internet. Plus, we have to save something for later - we're pacing ourselves for a lifetime of new sexual experiences. We don't want to become jaded, or bored. We also want to make our mums proud, or at least keep them from disowning us. And isn't it a little comforting to get your sex advice from women who haven't been there, done it all?

Still, as sex writers, we do get opportunities that would make the Joneses blush. We once taught a three-hour adult education class titled (not by us) 'How to Drive Your Woman Wild in Bed' and were faced with a sea of fiftysomething gentlemen in business suits with notepads and no sense of humour about the game of sexual jeopardy we made them play.

Another time, we got free passes to a workshop on how to shoot amateur porn and found ourselves in a crowded room of fiftysomething men in cardigans with notepads and a disturbing knowledge of child porn laws while two women went down on each other (so the instructor could demonstrate proper camera techniques) not four feet from where we were stuck in the front row.

When we stopped by our favourite sex-toy shop in San Francisco last summer, its publicist handed us a pen and paper and instructed us to write down every item we wanted to take home. One Sunday morning at 6am, we accepted an invitation from photographer Spencer Tunick to join one of his group nude shoots on the cold, damp bank of the East River. We held a book signing in the Bible Belt city of Raleigh, North Carolina, where one fan asked us to spank him with the book, another told us how she once had an orgasm just listening to music and another gave us our very own handcrafted glass dildos.

And for this very article, we got to while away an afternoon in a lovely hotel room staring at a charming, young, naked gentleman. It was about time Lo got to see an uncircumcised member in the flesh.

Days like these remind us that we're not Derrida, and the reminders ward off the occupational hazard we fear the most: that we'll start to take ourselves, or our sex lives (or yours), too seriously. Lo's been known to get pouty when phone sex doesn't go exactly as she'd hoped, and Em once told a guy: 'Then he does this to her' to which he responded: 'Me? You mean, then I do this to you, right?'

We sometimes catch ourselves leaning close into a reporter, stern-faced and intense, discussing the search for the elusive G-spot as if it were a weapon of mass destruction. We once read aloud from the anal sex chapter of The Big Bang at a coffee house in New York and we think we actually managed to bore people more than the woman who recited her angst-ridden, Bridget-Jones-meets-Sylvia-Plath free verse poetry.

People don't want to think that taking sex advice is hard work or - God forbid - dull. So we do our best to keep it fun and funny, both at work and at play. Now, when we're discussing backdoor friendship, we don flight attendants' outfits and pretend we're giving safety instructions to keep the audience's attention. And we're working on a free verse poem about fisting. No, it's not Derrida, but then again, who ever had the best sex of their life after reading Of Grammatology?

· The Big Bang by Emma Taylor and Lorelei Sharkey is published by Hodder & Stoughton, £12.99.

· Em & Lo will be part of a panel discussion on the Sex Package at the ICA, London SW1 on 29 April. For tickets and information, call 0207 930 3647 or see www.ica.org.uk