Reprinted from elsewhere on this board:
Your readers can always tell when you're bored.
Writing is a lousy make-money-fast scheme. If you aren't doing it at least a little bit for love, I can point to a lot of things that will bring you more money for less work.
Next: Observe this diagram
The area labeled "A" is what fascinates you; what you might write about. The area labeled "B" is what fascinates everyone else, that they want to read about. The area labeled "C" is what's marketable.
You can't guess this in advance.
Take, for example, Maureen F. McHugh. She was fascinated by Chinese people, gay guys, and subways. She wrote China Mountain Zhang
. This was her first novel, and it was picked out of the slush pile. It was published, remains in print, and led her to a career in mainstream literary novels.
The books you're seeing now as the Hot New Releases were bought two years ago. The trend as to who's buying what has already moved on. Write what's going to be on the shelf two years from now, not what's on the shelf today.