"Where do you get your ideas?" is the question put to authors a lot, and it's fundamentally the wrong question.
The ideas are always out there. They are almost irrelevant. If you're looking for them, if you're thinking creatively of how to integrate them to each other, you'll find them. What matters is how you turn that idea in to a story.
And that goes into how you're keeping your tank full.
By which I mean, as a writer, you should always be taking in input while you're making output. That doesn't necessarily mean Read All The Books--- but you should be reading, of course-- but any other thing that can fuel your imagination: movies, television, music, art, anything. That's what's going to give you the little bits that weave together to become new ideas.
And you need that. You can't keep driving on an empty tank. It never works.