11. Balance Your Training
Make sure you address pushing and pulling on both horizontal and vertical planes and attempt to balance the loading.
If you're bench-pressing 400 pounds, but can only do a chest-supported row with 50 pounds, your shoulder girdle is going to suffer.
If you can't handle the same loads for two opposing movements, then increase the volume of the weaker movement by doing an extra exercise or an extra set or two.
12. Get Out of the Weight Room
Try some other forms of training such as sled dragging, uphill sprints or running stadium stairs. The more varied and interesting the workout, the better chance you'll stick with the program.
13. Train the Antagonists
The speed of a serve or a forehand is determined largely by the ability of the antagonist (opposing muscle to main muscle) to eccentrically decelerate your joint action and prevent joint injury. If you can't safely and effectively slow down an action, then it will not allow you to achieve full acceleration.
If you're not training the antagonists, you're not training deceleration. And if you are not training deceleration, you can't be training acceleration.
Try catching and slowing down a medicine ball from your partner, just like you would you take it back into a forehand or backhand.
Remember, don't get caught up in the numbers game and don't confuse gym improvements with on-court improvements.
The greatest players in the world don't have the greatest bench presses in the world. They do have an ability to produce impressive force on the court.
Find a tennis tournament near you.