Coming up with startup ideas is a question of seeing the obvious

When you find the right sort of problem, you should probably be able to describe it as obvious, at least to you. 

It’s a weird process: you're trying to see things that are obvious, and yet that you hadn't seen.

What you need to do here is loosen up your own mind, and not to make too much of a direct frontal attack — i.e. to sit down and try to think of ideas. The best plan is to keep a background process running, looking for things that seem to be missing. Work on hard problems, driven mainly by curiosity, but have a second self watching over your shoulder, taking note of gaps and anomalies.