Specifically, when I started writing, I generally thought that story ideas arrived out of the ether, and one either got them or one didn't. Now, however, I've learned something interesting: Inspiration can be triggered.
I usually do it by researching, and chasing whatever threads catch my fancy; allowing them to knot up in the back of my head until a bunch of different threads suddenly come together and a story arises out of them. And some of it just comes from being open to ideas, and going 'oh, there's a story in that.' and then looking for the story.
And taking the first idea and throwing it out, and taking the second idea and asking "but what if?" and then taking the answer and asking "but what if then?" Because the good ideas come from conglomerations of things that haven't been stuck together in quite that way before, or from a fresh approach, or from--
--because everything has been done, yeah. But there are still angles and combinations that haven't been. And that's where the stories are. And I think it's as important to have fresh stories to write as it is to write them well. So googling on monkeys leads me to a picture of a samango monkey, which leads me to the Magoebaskloof Hotel, which leads me to some ecological information and a news story about a fire...
...and suddenly they're a story. Because I kept chasing that monkey.
Or a story on NPR about grafitti artists combines in my head with an idea about Drowned New Orleans and tattoos as caste marks, and suddenly that's another story.
I think it is very possible to train one's self to inspiration, too, because ten years ago I had a much harder time making those connections and coming up with those ideas. And I know both Waldrop and Bradbury talk about the story generating process in much the same way--cram the brain with interesting tidbits, and fiction is a natural side effect.
Life experience works too, but since it's necessarily more limited due to time constraints, it seems to generate less variation in subject matter for any given writer.
Also, I have a lot of clutter on my desk. I think that helps me be creative, too--no telling what might trigger an idea or a character detail. The Tiger Balm? Maybe. The Shakespeare finger pupper from quinnclub? The cheap Chinatown kaleidoscope? The PEZ dispenser? The Penguin mints?
Any and all of it. My grandfather's babyshit-brown Dodge Polara shows up in cameo roles a lot, for example. As does my mom's Opel Manta. *g*
So, yeah, that's my advice if you can't find ideas. Look, read, observe, live. Research. Handle things. Talk to people. Volunteer for weird jobs. And keep asking 'what if'?
On paper edits up to page 250 of The Startford Man, and I have up to page 119 input into the file. And I've gotten ten pages out of it as of page 119, mostly through more muscular prose and snipping the odd conversation digression or repetition.