I'm sure you know this already, but I think the best ideas and the ones that you will be strongly motivated to work on are those that solve a problem for a lot of people, but principally for you. Something in your business life or elsewhere that you have found frustrating or lacking, but that has no good tech solution. But I'm sure I read it elsewhere and it made sense that it's easier to find solutions than problems. Don't look for a solution, look for a problem, a tough one, then cast about for ways to solve it.