Our blog to accompany the 2013 Wellcome Trust Science Writing Prize asks top science writers about their craft.Today we speak to freelance science writer

What makes a good science story?

Something that is new, and interesting. Same as with any other subject. Who decides what's interesting? That's your call.

What do you need to know to write well about science?

You need to know something about how science works. Not reams of facts or figures necessarily, but you need to be able to spot an interesting story amid the ocean of white noise and misinformation and this means, as often as not, a basic appreciation of the scientific method, possession of a functioning bullshit detector, some appreciation of statistics and so forth.

How do you choose your opening line?

With care. With a feature you can meander a bit at the top but not too much. Drop your intro if you want, but not down a well so you can't see it. With any news story, you tell it once, you tell it twice, you tell it again. The ideal is to convey as much salient information about what is new, and interesting, in the first word. Failing that, the first sentence. Failing that, the first paragraph. In a news story, if you can't do that then you either don't have a story or you do not know how to write.

How do you get the best out of an interviewee?

Be nice and kind and don't stitch them up. Be aware that most people, especially scientists, are terrifyingly willing to open up to a journalist they have never met before. Ask straight questions. And do a bit of research: people respond poorly to being asked questions to which their answer is well known and in the public domain. Do not insult their intelligence by demonstrating the lack of yours. Face to face is best; then phone, then email. But even a text is better than nothing at all.

How do you use metaphors and analogies in a story?

Sparingly, but well. Analogies are de rigeur in physics stories – so much so that they become cliches (see the social life of the Higgs boson and its various cocktail parties). Don't be heavy-handed; the best analogies are introduced with a light touch.

What do you leave out of your stories?

Anything irrelevant. Anything I am told to put in. Anything boring.

How do you stay objective and balanced as a writer? Should you?

You don't, you can't and nor should you pretend that you are. Objectivity is an impossible thing to achieve so don't bother trying and forget the idea of a deep, objective "truth" that it is your job to expose.

All journalists have an agenda; the best make this clear to their readers from the off. Remember that your agenda may reveal itself simply by the sort of stories you choose to cover – and the ones you don't. This doesn't mean you cannot achieve a degree of balance and objectivity in individual stories; sometimes something is too close to call, or the jury is out. It is your job to reflect this. However, if you are writing about evolution (as opposed to Creationism) you are not demonstrating "balance" by interviewing a Creationist; you are demonstrating that you don't understand anything about anything.

What's the biggest potential pitfall when writing about science?

Succumbing to gee-whizz over-enthusiasm about a marginal piece of research is all too easy. We've all done it. Most "medical breakthroughs" are nothing of the sort. Indeed most are PR bullshit. And always make sure you quote absolute risks/benefits, not just relative. If something increases your risk of developing a nasty cancer by 30%, this is only significant if the absolute risk is substantial; if it is in the one-in-a-million category then it is not news.

If you are "linking" behaviour X to effect Y you need to explain at least a little of how that link works causally. Talking of which, understand that correlation does not imply causation – a basic truth that passes too many people by. Be careful with language; terms like "probable", "theory" and "hypothesis" actually have quite well-defined meanings to scientists, which may differ to the meanings accepted by non-scientists (and may well vary across various disciplines).

Finally, remember that when a Very Grand and Famous Scientist starts talking about something controversial outside their own specialism then he or she is almost certainly talking cobblers. A Nobel prize is no guarantee of common sense.

• Michael Hanlon is a freelance science writer.

• Read some Michael Hanlon – we like Fake meat: is science fiction on the verge of becoming fact? published in the Guardian in 2012.

• Find out more about how to enter the Wellcome Trust Science Writing Prize, in association with the Guardian and Observer, on the Wellcome Trust website – the closing date is 28 April 2013.