Another county heard from: Aliya Whitely, author of Three Things About Me as well as a shockingly extensive collection of other writings, has explained her storybuilding process over on her blog. (The blog, Pootle and Rat, is actually a duo-blog, I gather. I've worked out that Aliya is Pootle, but I'm not sure about Rat.)
I won't even attempt to summarize what she says, except to note that it's hilarious--and that it has the ring of truth. It also involves careful planning, but then--well, go read it for yourself.