I once wrote a short story about a schoolteacher who, in a bid to forget his unhappy career, launches into a newly invigorated sex life, thereby cheering and exhausting his wife in equal measure.

I didn't go into great anatomical detail, preferring to close the bedroom curtains and leave readers to their own thoughts, yet I was startled to discover that, when reading to a roomful of listeners at a book festival, what had seemed extraordinarily minimal on the page was not so easy to read aloud. Even odder was the woman who came up to me at the end of the event and said I had just perfectly described her last marriage, and had I been in one like that too?

Therein lie at least two of the many pitfalls of writing fictional sex in stories that are not intended as erotica. For a start, as Julian Barnes writes in last week's Radio Times, authors are terrified that people will assume these scenes are based on their own experiences. Admittedly, the likes of the incontinently priapic Edmund White, whose novels draw on his own adventures, have done nothing to dispel that theory, but throughout the history of fiction and poetry, this is the one arena in which it is probably safer to assume the writer is leaping into a world beyond their ken than re-reading their diaries.

A more understandable fear, however, is old-fashioned embarrassment. Partly this can be blamed on the notorious Literary Review's annual Bad Sex prize, which has been won by such as John Updike, David Guterson and Sebastian Faulks. No wonder lesser novelists hesitate as dresses and trousers slip to the floor, and quickly decide to let matters unfold in absolute privacy. Beyond an author's kilt falling around his ankles as he walks onstage to receive the Man Booker prize, it's hard to imagine a more wretched writerly humiliation than having a sensual passage torn out of context and held up to mockery.

In founding the prize Auberon Waugh, of course, was merely making comic capital out of an ancient affliction. Because as everybody knows, the main cause of failing novelistic nerve when it comes to sex is being British. Even today when older readers consider themselves sophisticated and unshockable, and a younger generation is being raised on internet porn, sex is still rarely deemed a fit subject for serious writing. When it is depicted, it tends to be pornographic, violent or romanticised. Such is the terror of being ridiculed that most writers steer so clear of specifics, it's a wonder fictional characters manage to reproduce at all.

There are, admittedly, some obvious taboos. No-one would argue with Julian Barnes's advice never to use vegetable similes in such scenes – he quotes one writer whose hero "felt his cashew becoming a banana", and it didn't stop there. But other than avoiding cliches, off-puttingly clinical language, ridiculous similes and a surfeit of gushy adjectives, it seems to me that the only good advice to writers who are wary about tackling such scenes is to write and read more of them.

Some years ago I criticised a Jilly Cooper novel for unconvincing sex scenes, and received a charming note saying she was now too old to write them. I felt bad, not least because sex is too easy a target for reviewers, a cheap way of raising a snigger at the writer's expense. Of course, sex scenes can, and sometimes should, be funny, as Cooper well knew. But poking fun at those that fall short merely reinforces the idea that sex is too dangerous to write about.

Yet by avoiding this vital facet of human life, writers risk diminishing their characters and their plots. It was Waugh's intention to discourage the gratuitous use of sex in novels, which was fair enough. But a better mission, surely, would be to encourage well-portrayed, realistic and meaningful literary sex. Perhaps those unnerved at the prospect should approach such scenes as if they were embarking on a new love affair: with reckless abandon and not a moment's worry about what anyone else thinks – even when reading at book festivals.