I have to know where it's set, what the problem is and I have to know whodunit. Then I start to do character sketches of the people who will be in the book. And I do background material. For example, for the last scene in this book I needed an apartment building that had an outside fire escape, so I went up to the neighborhood where they have them. These are things that are important.
Little details start to make a story valid.
I rewrite all the time almost to a fault. I finally decided to go back to it later. I do a great deal of rewriting but chapter by chapter. That works wonderfully for me. On this book Michael said don't show that a particular character is still alive, it would be a mistake.