Sometimes things come to me just out of nowhere.
Also, when I'm working on the art for my comic, I'm usually listening to something like an audiobook, or watching some television series on Youtube (often cartoons), and when something pops up that I think I may be able to use, I write it down in a notepad document.
I usually present the concepts my own way, though, so they never wind up being direct copies of whatever initially inspired them. So yeah, read a lot, watch a lot, play a lot, take what will be useful to you, and put your own spin on it. I've found that method to be very effective.