There are certain questions that writers are pestered with all the time. The answerability of these questions varies inversely with how often the writer is asked: for instance, the question "where do you get your ideas?" is virtually unanswerable yet is the most FAQ of all, whereas "are you really a whole and separate human being with thoughts and opinions of your own who is not to be mistaken with the lead character/serial killer/transvestite in your last novel?" is very easy to answer but nobody ever seems to ask that one.
Somewhere between these stools (and you may apply either definition of the word there) lies that question beloved of lazy interviewers, "who are your influences?". It's a lazy question because it fails to establish a premise for an answer: after all, what exactly constitutes an 'influence' on a writer? Strictly speaking, everything is an influence on the writing itself: a writer who is not inspired, driven or in some way affected and provoked by the world around him is not really a writer. Even Pratchett, about as divorced fictionally from the real world as one can get (Discworld is FLAT. The clue is in the name), permeates his work with observation of our mundanely globular planet. A lot of writing isn't really inventing stuff to put in, so much as filtering out the stuff that isn't needed.
Generally speaking the question of influences is expected to be answered with a list of names, usually of other authors. This too is a flawed approach since it doesn't get to the bone of how or why these people (or, more accurately, their writing) influenced you (or yours) - it seemingly serves only to reassure the casual magazine-reader that actually that lauded novelist pinched half his ideas from some other guys. It's okay, thinks our reader, he's not all that talented after all: he just read a bunch of books and replicated what he saw. I could do that, if I weren't so very busy doing fuck all with my life.
I consider Colin MacInnes to be the strongest influence on my work and (to my eyes, anyway) the most obvious: strongest because his book Absolute Beginners - which I read when I was in my early teens, when all my writing ambition was leaning vaguely toward journalism and (I'll explain this another time) rap music - was the one that showed me how the magic combination of intent and style can tell truths more potent than simple facts could; obvious because I still show a few of his bad habits in my writing, especially a surfeit of commas, which I adore. I have always wanted to write in order to communicate a truth of some sort and this urge took me to journalism first as I thought truth to be inseparable from fact: Absolute Beginners is more true an account of London in the late Fifties than any history book I have read, truer a description of the teenage mindset than Anne Frank's bloody diary. This is a trick that a good novel alone can pull off. Facts can get in the way of truth, which is why so much journalism is either fabricated or bunk, but rarely both. In any case, Colin (along with Anais Nin) is one of the very few people I honestly regret never having met while they were alive.
Neil Gaiman, on the other hand, has influenced my choice of subjects and my imagination more strongly than any other writer. Most writers can invent a world and bring you to it in a book: very few can actually extend the reach of your imagination and genuinely broaden your horizons. Neil does that, and employs a deceptively simple style of writing that I find enthralling. That said I do not try to write like him: I love complexity, enjoy the juggling and tangle of narrative too much to pare it down to the haiku that Neil does so well.
On yet another (third, and therefore imaginary) hand, there is Conn Iggulden, whose Emperor series I simply cannot stand: I find those books unnecessary and uninspiring although to be fair I tend toward that feeling about nearly all historical fiction. His novella Blackwater is very different in tone and much, much better: reading it made me feel (and I cannot say whether this feeling is in any way accurate - I have met him, once, through a mutual friend, but we had little to talk about and our paths have not crossed since) that this was the kind of writing he really should be doing, that he really wants to do. Blackwater isn't perfect (the only perfect novella I have read is the breathtakingly good Reunion by Fred Uhlman) and it's certainly not commercial in the way that Emperor irrefutably is, but it has that truth that I spoke of. Conn's writing influences me in a totally different way - it gives me something to aim at, something that I am sure I can exceed in quality that has become very widely read. Conn proves that It Can Be Done, and this could well be the most crucial way that an author can be influenced. I really hope that Conn writes more contemporary fiction in future, because Blackwater is lit from within.
Then there are (on yet more hands. I am starting to look like a Hindu deity at this point) people like Grace Dent and Tycho from Penny Arcade, who have directly influenced my style on the page by making me loosen up a little over my use of italics. Actually, Grace tends to favour emboldening instead, at least on her RT blog, but the principle is the same. I could go on, but I fear the bloating of my ego that results from too much time spent talking about myself.
You see? No easy answers. Don't even ask where I get my ideas from. I will only be sarcastic.