Talk to people. Tell them you're starting a company. Lay out an idea. It doesn't have to be good. It's been my experience that this scenario triggers an irresistible impulse in the other person to tell you _their_ ideas. Sooner or later, you'll hear something interesting. Explore it and refine it.
The biggest mistakes you can make, IMO, are (a.) thinking your idea is too stupid to start with, and (b.) keeping it a secret. The idea you start with almost certainly won't be what you finish with; the important thing is to get started. And if you don't talk about it, you'll never really explore, refine or (as you'll almost certainly need to) abandon it for something better.
Most people have something interesting to say. Find out what it is.
The biggest mistakes you can make, IMO, are (a.) thinking your idea is too stupid to start with, and (b.) keeping it a secret. The idea you start with almost certainly won't be what you finish with; the important thing is to get started. And if you don't talk about it, you'll never really explore, refine or (as you'll almost certainly need to) abandon it for something better.
Most people have something interesting to say. Find out what it is.