Janice Hardy has a brilliant post this morning about her writing process. It's impressively structured and organised, so if you're like me (I am the Queen of the Seat of the Pants) I recommend you read it more for editing advice than writing advice.
My method is to spew at the page and then chip away the bits that aren't book - an unnecessarily painful method, actually, for someone with separation issues ['Noooo - my darling paragraph. I cannot bear to let you go! I know you deal with my protagonist buying milk and are written entirely in the passive voice, but that is no stop to true codependency!'].
Janice's post is going to be very helpful with my chipping process. And if you're less seat-of-pantsy than I am, it will definitely help your writing.