Scenario: You are playing doubles and all four players are at the net near the service line or closer. Rule #1: Hit the difficult shots, (the ones where you are off balance, a little out of control and the ball is low) in the direction in which you are falling. Thus, if you are falling to your left, hit the ball to the left. If you are falling to your right, hit the ball to the right.
Why does this work? Because... when you move to the ball your partner will flow with you. So, for example, if you receive a difficult wide shot up your alley and you hit it cross-court, you have left your partner's alley completely open. When you hit it up the line in the direction you are falling, your partner will be where 70% of the balls are hit in doubles, down the middle. She will have moved towards the middle to cover it as you move to hit the wide opponents' shot. This will also give you more time to get back in the point.
The Problem: Low balls down the middle, between you and your partner. Remember, by hitting the ball in the direction you are falling you are hitting the ball over the lowest part of the net and you are already covering the middle if the point continues. Just try to restart the point here, not trying to win with it.
Remember, do what you want with the high balls, you are on the offensive. In the defense, be patient with the low difficult shots. Just try to neutralize this shot and restart the point.
Try this rule when all four players are at the net and you are hitting in an "off-balance" position against a difficult ball.
Good luck on the courts!