The player who wins long rallies is the one who can place his ground strokes where he wants them.
A good drill for sharpening your shot placement is to practice in the doubles alleys, down each side of the court.
The next time you're working on your game with a tennis companion, move over into one of the alleys and hit ground strokes back and forth. Try to keep all your shots between the lines and in the alley.
It won't be easy at first. The alley is only four and a half feet wide, and the net is higher out there. There isn't much room to aim for.
But striving to hit the ball in the narrow confines of the alley will develop your accuracy and make it seem much easier to hit bigger targets when you return to playing the entire court.
To make the alley drill more fun, you can play points or see which of you makes more shots in a 15-minute period.