Draw some more
Most of what comes out is pretty terrible stuff. I'd say maybe one drawing in 6 comes out as something that could be used as a final image that I'd want to show to someone. These drawings are normally in sketch books, or on loose sheets of scrap paper I have squirreled away. I usually start drawing with no real idea of subject matter, unless I'm sketching from life. Gradually, as one drawing leads to another, I'll sometimes notice a recurring theme that I hadn't even thought about. If it's something cool, I can try to develop more drawings in the same vein.
I'm heavily influenced by whatever I tend to be reading at the time, or whatever artist I'm "into" at the time. Lately, I've really been enjoying the work of Helene Schjerfbeck, and that's led me to try portraiture.