I tend to sit down and work, which is usually the best place for ideas. If they come to you in the shower, or in the supermarket, they're generally a nuisance because you can't write them down immediately. I'm sure all authors are different, but for me it's an evolving process which takes place mainly at the desk by writing and writing, and seeing what develops. That said it's true that once a book is under way it becomes the over-riding obsession, and you think about it fairly constantly, but I never try to kick-start the process by sitting down and deliberately sketching a character or a story that might be useful. When a character comes along I let them develop as they want, and likewise the story. I'm on Chapter Three of the 3rd Alfred book at the moment and genuinely don't have a clue how this chapter will end, or what will happen in the rest of the book. To me writing a book is like climbing a mountain - you get a quarter of the way up, turn round and see a much better route, at which point I start again, using the new route, and that provides impetus to get halfway up, or a third of the way up, when you repeat the process. The most important thing, though, is that telling stories is intensely enjoyable - whatever way you do it.