If you spent five-ten minutes each day shadow practicing your strokes and footwork, you'll be surprised at the improvement, not to mention the health benefits. Make it part of your fitness regimen. For example, every day do 50-100 forehands, backhands, forehand loops, backhand loops, and side-to-side footwork, alternating forehands and backhands or just doing all forehand, side to side. Adjust to your own style of play, i.e. if you mostly loop the forehand, do lots of forehand looping shadow practice. If you are a chopper, do lots of chopping. Vary the routine to include other moves you use regularly, such as shadow practice stepping in and flipping a short ball to the forehand, or a forehand loop against backspin followed by a smash or loop against topspin. When no one's watching (if you're shy), play out points as if they were real!