You just write everything down that you can dream up about the story. Don’t worry if the early drafts don’t make sense. You need to write and write until you understand the characters and what wonderful and horrible experiences they’re having, as well as what their relationships are like and how all those things change their lives. Once you’ve nailed that down, start revising so that the scenes unfold in a logical and satisfying order.
Most of my books go through 8 drafts. Nobody sees the first 5, including my editor. Especially my editor!
(from Laurie’s Goodreads Q&A)