I'm always seeing art styles and places I want to rip off make something like. Sometimes I'll take a walk on Google Earth or in real life, around town, and ideas for scenarios and places will come into my head. I never outright plaigarise anything, unless it was something that actually happened, or if it's too similar, I credit the original.
I also find I have more ideas the more eventful my life is. Sitting and waiting for them to come doesn't work, and a lot of my games are set on Earth, or inspired by reality.