I just try to think creay tiv lee.
For realzies though I like to try and start off with something thats really really dumb and then fix it up from there until I think it's good, it's always easier to edit something til its good than it is to come up with a great idea.
For example, an initial idea might be something really stupid like "what if flies could talk?" and then I'll mull it over in my head for a good while until it develops into something less dumb. Perhaps in its final version it's a psychological horror story about a guy who suddenly can hear what flies are saying? Or maybe it's a goofy animal slice of life with a fly-person as a protagonist? Maybe I'll do some research on flies to find out an interesting fun fact that could spin off into it's own set of concepts (They only eat liquids! Maybe the fly guy is on a juice cleanse, or they're an alcoholic bartender?)
Eventually after mulling it over long enough I'll have something that I might wanna actually put in the hours/weeks/years to turn it into a real thing, and during that process of making this initial idea into a comic I'll probably come up with even more ideas for it, and for other future projects.
So many people shut themselves down before they even give their ideas a chance to develop, because they think they're dumb or that they can't make a thing about XYZ. The truth is is that no idea is good or bad inherently, it just depends on the execution of it. If you make a comic about an alcoholic fly man it will look really really different from the version that I make. That's just how creativity works.