There are a number of writing prompts that can be used to overcome writer's block or just stimulate creativity. A popular one is timed writing. Just keep the pen moving, without analyzing, rereading, or editing, for a set period of time. Sometimes surprising things can come out of such an exercise.
Another trick is to go to a public place and write down the conversations you hear. I came up with a variation on that theme, which I call the channel surfing prompt. This works best if you have access to a large number of stations through cable or satellite dish. Put the TV on a station and as soon as you hear a complete sentence, hit the mute button, and write down the sentence. Go to the next station and do the same. I did this till I had filled up a couple pages with random sentences. Then I tried to pull out some of the sentences to write a piece of fiction or poem. I wouldn't say this was a wildly successful effort, but I think it has potential, and I will try it again. It might even be more interesting if I don't limit it to complete sentences. This is a work in progress.
Another prompt I have read about is to write a letter to someone--a friend, and enemy, a relative, one of your fictional characters (or have the character write a letter to you). As a variant, I am writing a talk-show style interview with my deceased mother. I'm not sure what, if anything, will come out of that, but it is stimulating a lot of memories.