I've found doing content gap analysis effective.
You could use keyword research tools to scan competitors and find topic clusters you'd like exploring. Or, simply going through archives/start here pages/popular posts for general ideas.
I usually let those ideas 'mature' for a while before swinging back around since the time between I'd likely explore the topics.
I love this idea!
I agree that's a really good technique too. You'd never run out of topics that way as long as you keep up the research.
I always envision my ideas "percolating" rather than maturing. But that just shows how old I am!