my way is very close to zerohour's. i'd add music heavily influences me. i tend to imagine every scene just like i'm watching a movie, then do my best to describe what i fantasize about. for me it's important to add some little detail that's interesting in most of the scenes.
i don't sit down with a theme in mind. nor do i try to use symbolism or allegory or some grand metaphor. most symbolism is so heavy-handed and obvious that i'm embarassed when i don't see it, and don't care for it when i do. i just want to tell an entertaining story. i'm not trying to write a book for the ages, necessarily. i've *done* the themes and all those things, i just don't care to ponder them. if there's any higher truth in anything i've written, it's bound to be accidental.
i rarely outline. when i'm just starting a project, i skip around in it quite a bit. one scene suggests another, and so on. if 'welcome to the jungle' pops on the radio, well, that scene is gonna kick ass and the rest of the book will just have to adapt. i keep it very loose and have to have challenge myself early on with a situation or mystery that i have to figure out. the harder the better. more often than not this boils down to purely a character motivation issue.
once i have a lot of scenes together, i'll put them in order then start thinking of how to connect them. generally speaking, in my mind, there's usually only one way a scene can logically happen, and there's only one way to follow that up. i feel that's one of my strengths as a writer, that i rarely get stuck for very long on just how the story blooms, and when i do, no big deal, i'll just skip ahead somewhere until i figure things out.
i probably practice the worst writing habits imaginable, heh heh. at least when i've got a story i'm hot on about, that's just about all i think about.