My recommendation is that you should start with a problem you are passionate about. Quite literally, I keep a notebook of stuff that annoys me. Then, every night I review it and try to coalesce it down to the essence of a problem. Youll find that youre probably passionate about 5 or 6 of the problems you come accross.

Fix one of these problems for yourself and 99 times out of 100 someone will be willing to pay for it.