Both Say and WildVolley make great points above.
Here is a link for the thrower's ten - probably the best set of exercises for shoulder/forearm health:
Do you practice "periodization"? That is do you emphasize certain aspects of strength training at different times of the year?
"Periodization of Tennis Strength Training
If you haven't heard the term before, "periodization" sounds complex. But it's a very simple principle that separates strength training for sport from the countless bodybuilding and general fitness routines out there.
Periodization is simply a way to break a larger training regime into smaller chunks or periods. Each period might be a mini training program in and of itself lasting 6 weeks or more.
Each has its own objective and one period follows naturally on from the other.
Unlike many sports, tennis demands several different types of strength... in particular muscular endurance and explosive power. And before these can be developed to optimal levels, the athlete needs to first develop good foundational and maximum strength.
If you try and train for every type of strength at once you'll end up with very little of anything - except fatigue!
So the best method is to focus on one type of strength in each separate phase. That way, you can easily maintain your gains during the competitive season.
There are no hard and fast rules to breaking a training program up into periods or phases.
The determining factor is when YOUR tournaments occur and when your season starts and ends.
Here are the 4 phases for this tennis strength training program example:
•Off-Season - 6-8 weeks
•Early Pre-Season - 6 weeks
•Late Pre-Season - 6 weeks
•In-Season - 3-4months"
Check the above link to learn more, including specific regimens.
Many cycle through various phases of strength training during the year, modifying it to accommodate their specific tennis schedule.