I'm starting a new novel, so I'm particularly fascinated by different writers' processes for this stage of the work. I'd heard a lot of praise for Randy Ingermanson's "Snowflake" method, but hadn't actually gone to the source until a few days ago.
The gist of Ingermanson's method is that he starts small, with the basic elements of the story, and then goes back and expands each small piece into bigger and bigger units, until they make up a whole novel. The name of the process comes from the image of starting with a simple geometric shape, and then expanding each point into several smaller points, until you end up with a "snowflake," that has all sorts of detailed little branches in all directions. It has the virtue of making a huge project (400 pages! Multiple characters! Plot twists and turns!) into more manageable bites. Ingermanson does a great job, too, of finding the excitement in each of the interim phases, so none of them seem like drudgery, even when they take a good chunk of time.
I do something similar in my writing process for a novel, but I call it the Pizza Method. I start out with this lump of dough (the premise of the story), and then I roll it out into an ever-expanding circle (the narrative outline that keeps getting added to as I figure things out), until it's the right basic shape and size for a pizza (or novel), and then I top it off with all sorts of yummy things (the final details of the story).
I could go on with the metaphor -- the first draft needs to sit and rise for a while before the toppings are added, and you always want to use the best ingredients -- but I think I'll stop now.
And go get some pizza.