My ideas come from a black hole inside my head... it eats everything up, and then, once in a while, explodes in a plethora of random ideas that somehow make sense.
But really, I usually end up by getting inspired by an image, a phrase, a concept and just let my imagination run wild. It often happens when watching or reading... I might just find a scene, an image, or a phrase, that just pulls the right strings in me... it can be something very small and insignificant, but if it hits the right cords, a whole story will just flood my mind.
And the funniest part is that it will be completely unrelated to the movie, book, scene, story, etc. Like I said, there must be a black hole in my head