When I pack up my camera gear and head out to take pictures, more often than not, I don't really know what I want to take pictures of, and those are the days I seem to take my best photos. There are the rare exceptions to that rule as well of course. One of my favorite photos to this day is one that I had thought about, days before actually taking the shot. I had this image in my head, and that image just kind of percolated in my mind for a few days. I found myself looking around to see if I could spot that shot everywhere I drove, trying to see if I could see something that would capture the feeling I had in mind.
After a few days, I decided I just needed to grab my camera and hit all the parks I could think of and try to capture the shot. The first couple of parks I stopped at just didn't look or feel right, but then I went to a park out near a house I rented years ago, and there it was. I'd never been in that park before, but the minute I walked down one of the paths, I knew it was the shot I was looking for. It didn't really matter if it was going to be a great shot or not, as this was just one of those photos I had to take for me.
Where did the inspiration for that shot come from? I really can't tell you. I don't know myself. But I think as you take more and more photos, you'll find that there are times where you find you're just in a certain kind of mood, or maybe you hear a song or watch a movie that makes you feel some emotion you just have to try to capture somehow... when you feel that... use it to inspire you to look around and try to put into a photograph.
Does that always work? No... but sometimes, you might just take a picture that you yourself can't stop looking at.