I'm not very prolific, but lately I've had luck starting with a little bit of a musical phrase, and then finding a verbal phrase that seems to hold up to repetition. Something simple. Then verses seem to unfold from it. I'm working on one about a situation in a Bertol Brecht play my wife was in years ago, another about holding onto things you can't throw out, and one I'm not sure what it's about yet--the central line changed after the chords and tune came together.