Apparently someone asked Robert Sawyer not too long ago, how he went about writing his Neanderthal Parallax trilogy, which I consider to be quite good(he won several awards for it). In today's post on his blog, he goes into cosiderable detail, from vague idea(it kept changing --- that's certainly a familiar feeling for me!), to book proposal. It is quite detailed, and is also very much worth reading, just to see how still another writer goes about creating his or her work of art. It is also interesting(and perhaps instructive) to also take a look at Elizabeth Chadwick's latest blog so you can see her writing process. In this case, she is just barely into what she is working on now.
I should add that while I don't think Robert Sawyer did enough research about Neandertals(his picture of them is rather more one-sided than the latest research about them would suggest is the case), he's very good at integrating what he did learn into a decent, readable set of novels. Elizabeth Chadwick's research is more or less ongoing, since she has made a kind of specialty out of her investigations into the family of William Marshal, which seems to be leading to some very interesting and readable stories.
But the point here is, there is a process; any aspiring writer would do well to look at these two blogs, for in both cases, the process that is going on is quite similar.