Most of tennis is about the exchange. What is this? Anytime you are warming up or just rallying the ball back and forth you are exchanging. Exchanging is very important! In a match where you have never played your opponents before, there is often a process going on where balls are "exchanged" just to see how they handle them and testing their strengths and weaknesses.
 
Usually when you are on the baseline, you are in "the exchange." What are the greatest mistakes made in the exchange in doubles? The #1 mistake is trying to win the point and the #2 mistake is making an unforced error. What you are waiting for in the exchange is an unforced error from your opponents. That's #1. After that, you are looking for "the change." Typically the change is the short ball. Either you hit it short on purpose or by accident or your opponents hit it short. The change is when you typically "go for" or win the point.
 
When you see your partner in the change you are also in the change. You can apply this information to volleys. When you are being attacked or receive a difficult shot at the net, see this as an "exchange." Just try to get the ball back and restart the point. However, if you are at the net and receive an easy high ball, this is "the change." Be aggressive and go for the point.
 
You usually cannot serve continuous aces or hit constant winners off your serve returns. Group these shots as "exchanges." It is very difficult to win a match when your partner constantly tries to hit winners from the baseline or makes constant "unforced errors."
 
Remember, every time you are warming up or practicing you are "exchanging." When the match starts don't forget this. Quit over hitting and over trying in a match.
 
Good luck on the Courts!