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 PratchettHowever, you do need rules. Driving on the left (or the right or, in parts of Europe, on the left and the right as the mood takes you) is a rule which works, since following it means you're more likely to reach your intended rather than your final destination.
Terry PratchettThis man was so absent-mindedly clever that he could paint pictures that didn’t just follow you around the room but went home with you and did the washing-up.
Terry Pratchett