Practice. I hit a few hundred balls a week when I don't play, and I enjoy trying new things, changing my grip slightly, adjusting my stance, etc., to see what happens. Last time out I shortened my backswing, and, understandably, I hit the ball more solidly than I had for a while. Being able to affect changes on the range helps to put those changes into play on the course when different shots are needed.
Beyond all of that, I wish that I had the time to play more than I do.