If you're between writing projects or find yourself at a loss for what to write about, try keeping a journal. Since it's only for your eyes it can have anything in it, but consider it as a place for any number of notes and ideas that you can develop when the time is right. Mine began in the early '80s when my family first came in close contact with Cambodian refugees in the Lowell, Massachusetts area. I'd had nothing in mind at the time, but the notes came in handy when I began writing fiction later in the decade.
If you don't know how to start, the web has some good resources such as http://www.wikihow.com/Keep-a-Journal.