Hello, my name is Kit Whitfield. I'm a writer who lives in South London. I have straight, silky hair, falling down to my shoulders in deep copper drifts. My skin is pale, and my hazel green eyes change colour according to the light. My lips tend to part, two pink anemones over charmingly crooked teeth.

Well, you see, all of this is reasonably accurate. I do have red shoulder-length hair, hazel green eyes, fair skin, and teeth that are reasonably straight (but I suspect that some Americans are reading this blog and there are masterpieces of Modernist architecture that look crooked next to an all-American smile). But it's a bit of a weird way to introduce myself, isn't it?

Yet somehow, a fair number of fictional characters do just that.

Such descriptions tend to dwell on the attractiveness of the characters' appearance, either traditional or non-traditional but still charming, and this is a warning bell right there. Unless a character is terribly vain, in which case we're looking at an unreliable narrator, who talks about themselves that way? Flattering self-descriptions create a horrible viewpoint lurch, because what they do is leap outside the character's head, and start looking at the character through what the author hopes will be the admiring eyes of the reader. Rather than letting the reader work out what the character looks like, or even get on with the story and assume that appearance isn't the first thing you need to know about someone - perish the thought, the situation they're in might be more interesting than their face - the writer makes a swift foray into the reader's viewpoint, firmly establishing that the character looks a certain way.

Of course, physical appearance is the first thing you notice when you meet someone. But when we're talking about first-person narrators, we're not exactly meeting them. In effect, we've woken up in their heads one morning - and the first thing you see when you wake up is not your own face. You see your bedroom ceiling, the face of your lover, or possibly the edge of a gutter and two hairy thugs standing over you and going through your pockets, if it's not your lucky morning. In any of those circumstances, whether you're blonde or brunette is not the most important question.

This extends beyond first-person narratives to third-person-single-viewpoint narratives. When an ominscient narrator introduces a character, external description is fine; Middlemarch begins with a prolonged description of Dorothea that is an incidental character sketch. But if you're writing a book where your heroine Rachel does this and does that, and we never see a scene that Rachel isn't present at, and everything is viewed as 'Rachel saw such-and-such' (with possibly the odd view into somebody else's head, which it's time you cleared up), then in effect, Rachel is occupying the first-person slot. We can't see her from the outside, because we're inside her head.

So what is a good way to present a character's appearance? Well, the first thing to do is ask yourself if it actually matters. Not just matters to you because you personally see the character as having dark curly hair and brown eyes, but matters to the story. It can do. The only female detective in a mean-streets squad is going to be judged on her attractiveness by most of her colleagues, so the fact that she's blonde and may be mistaken for a bimbo, or has mousy-coloured hair that makes people assume she's meek and dull, will have an effect on how people behave towards her. A man who's six foot seven will probably get more deference than a man of five foot two, and will possibly have developed a carefully gentle personality so as not to make people feel threatened. A woman whose body weight is twice what the doctor thinks it should be will be profoundly self-conscious and also have more difficulty moving around quickly.

But all of these examples are things that you can show in other ways. They're things that can be seen and commented on by other characters because they actually would draw comment, rather than just because the writer wants to make sure everyone knows what their hero looks like, or they're things that would affect a character's behaviour and so be factored into their thoughts when they make decisions. There's no need to go into detail the minute the story starts.

As a side-note, 'drawing comment' doesn't mean sneaking the observations you can't have a character say about themselves into the mouths of other characters. Nobody says 'her skin is as golden as honey and looks every bit as tempting', I don't care how nice the image sounds.

Another way we can find out things about a character's appearance is at points where they see themselves. If a woman with long hair rests her head on her arms, the chances are that some of the hair will fall over her eyes, at which point she will notice what colour it is, for instance. The use of mirrors is one to be wary of, though, as it's incredibly easy to turn it into a cheat. If a character checks himself in the mirror and thinks, 'I think I'll wear this jumper so my date doesn't see how weedy-chested I am,' that's relevant to the story, but if he looks in the mirror and thinks, 'Hmm, I have brown hair and grey eyes, I'm five foot ten but very thin and feeble-looking,' then the reader is going to snag on it, because nobody catalogues themselves that way.

(Unless, of course, the character has serious body issues. In which case, they're likely to keep track of themselves throughout the story, with regular weigh-ins, checks to see if the hairstyle needs adjustment, changes of clothes, manicures on the run or whatever else their particular obsession involves. Again, appearance is related to personality and personality is expressed through behaviour.)

Scientists talk about the 'halo effect': the fact that attractive people tend to be considered nicer, cleverer, more competent, and generally get a more positive spin put on their behaviour than unattractive ones. This effect, however, doesn't exactly translate into writing. The writer may be able to picture the character precisely, but the reader can't actually see them. All they get is the words on the page. A handsome face may make a movie character seem deeper than the script actually portrays them as being, but in fiction, the physical description is just more words. In which case, when you describe the character's looks, you don't get a 'Mm, that's a nice-looking person', you get 'why are you telling me this?'

And if you can think of a good reason, then you're fine. But if not, then maybe we don't need to hear about that hair colour or waist measurement at all.