There's just one thing you have to do -- think.
Just always keep your eyes open to the things that don't work as well as they should, and work to improve them. Just start. Start small. Build out the core, then go bigger. Let it consume you.
A million great ideas come out of any kind of work you feel passionate about. Just find something that sucks and improve it. Once you get the ball rolling you'll have more ideas than you could build in a lifetime.