As you approach any major intersection, you will see a traffic light with yellow, red and green colors. The red light standing for "STOP," the yellow light standing for "CAUTION," and the green light standing for "GO." You can equate this traffic light to tennis.
Yellow zone shots may include low volleys, half volleys and deep lobs.
Green zone shots may include easy high volleys, short overheads, bounce smashes, kill shots (short high bouncing balls hit near or inside the service line) and first serves.
Red zone shots may include shots received when your opponent is attacking you from a green zone with a very aggressive shot.
Remember, when you are in the yellow zone do not "force" the point. Try to return these shots in such a way that you force your opponent to hit out of a yellow zone. Hitting slower out of the yellow zone will be a great aid in helping keep the ball low. In the green zone "Go." "Go" win the point. Be aggressive.
In the red zone (when you are being attacked) move back as far as you can, then STOP. Try to return as many shots as you can in a defensive nature. Any shots you can make when you are in the red zone is like a bonus.
In general, you will not usually win the point when you are in the yellow or red zone. You will definitely go for the point in the green zone. A good goal is to make your opponent try to win out of the yellow and red zones, while you would love to play a majority of your shots in the green zone. This way you will win as a result of winning points in the green zone and receiving errors from your opponent as he hits out of the red and yellow zone.
Good luck on the court!