Skill and technique are more important than anything in Tennis but by strengthening your body you will be able to run and shoot faster, so strength training is definitely important for this sport. Even a sprinting increase of a few milliseconds can make a difference and the harder your shots are the harder it will be for your opponents to keep up with you.
Upper Body Training
Probably the best strengthening exercises for tennis players are the ones which utilize a kettlebell. These exercises are a mix between a strength building exercise and a cardiovascular exercise.
The Single Arm Swing: This exercise will grant you more power and improve your serve. To execute this lift simply pick the bell up off of the ground with one arm. Next, rotate your fist so that your knuckles are pointing right at the sphere of the bell. From here on simply swing the bell between your legs and up to chest level. Make sure to properly utilize your hips in order to build the momentum to swing the kettlebell.