I once read an interview with prolific, bestselling author Daniel Pink. He said people often ask him how he decides what to write next. His answer, in a nutshell: when an idea for a book comes to me, I try to forget it. If I can’t forget it, I know that’s the thing I must write about next.
I have files and files, docs and docs (electronic, of course), filled with ideas for books. Most of them I’ve forgotten. Some of them I remember. Many of them are, frankly, kind of embarrassing. As in: Did I really think that would be a good book idea? Ick.
None of them occupy my writing time until they move into the realm of ideas I can’t forget. Characters who wake me up at night “speaking” to me about the narratives of their lives. Story lines that randomly enter my mind and which I must quickly capture because I know I’m going to do something with them.