I've said this elsewhere, but I think I oughta elaborate on it here a bit: The first rule of creativity is, feed your head.
You need to stuff your brain full of inspiration - read more books, go to more movies, listen to more music, talk to more people, travel to more places, drink more booze. Then let all the input rattle around in your subconscious. You might just be surprised at the result.
Case in point: I haven't been creatively blocked in years. I've got notebooks and sketchpads full of untapped ideas that could keep me going for a long time to come. Surely I can't be unique in this regard.