I certainly don't sit down and plan a book out before I write it. There's a phrase I use called "The Valley Full of Clouds." Writing a novel is as if you are going off on a journey across a valley. The valley is full of mist, but you can see the top of a tree here and the top of another tree over there. And with any luck you can see the other side of the valley. But you cannot see down into the mist. Nevertheless, you head for the first tree.
Terry PratchettAny wizard bright enough to survive for five minutes was also bright enough to realize that if there was any power in demonology, then it lay with the demons. Using it for your own purposes would be like trying to beat mice to death with a rattlesnake.
Terry Pratchett