When I write a book, I usually have a very clear idea of the world, most of the characters, and the beginning, a scene in the middle, and the ending. I let the rest be created on the fly, so to speak. A process than writers call "pantsing," or flying by the seat of your pants.
For Destroyer of Legends, one of the two books I'm working on now, I've decided to try outlining the entire book first, then filling it in. It should be an interesting experiment, and I'll let you know how I feel about it vs. my usual method of writing my novels!