I think about what I'm feeling passionate about; what I feel I have something to say about. Sometimes I look back through things I've written about that I've kept over the years. I'm a writer by profession, and many times when I've written things they were not published, so I have a lot of stuff that just needs tweaking and updating. Still, even though I have all that, many of the articles I write are about things I just feel a strong need to write on. Then, after researching the topic, I begin writing. When I'm writing fiction, I have to wait until my "muse" shows up.