Ideas come when you are in a really difficult position and need something urgently. You try to find solutions for that problem by trying to see if there is a solution for your particular problem out there. If the solutions out there don't solve your problem, then you come up with your own. Because if the current solutions are not working for you, you can bet it is not working for someone also.

Don't look for an idea just because... If you do that, your enthusiasm for it will/can wane. But if what you are creating solves your own problem, wakes you up at 3am because you are too excited to finally figure it out then you may be unto something.