I do something called "free writing," jotting down random ideas that come to my mind. Some of them turn out to be something I can use. James Scott Bell has a great idea in "Plot and Structure." He looks through a physical thesaurus and finds 2 random words to spark a plot idea. For example, I chose "exterior" and "red" in a random fashion. If I were a suspense writer, maybe the hero sees red makings on the side of a barn. I could go on with this. Walking away from the computer for a while also helps.