I love H.S. tennis coaches that think this is they way to go about winning tennis matches. Since that's what he does, you need to start running. Go for a mile run on your treadmill or with your dad every other day. Gradually build up about a 1/4 mile every other day.
On the day your not doing a distance run, start doing some wind sprints. You may have done them before. Have your dad or someone hold a stop watch and push you though the windsprints for about 10 minutes the first week. Then build up to 15 the next.
Be sure your cool down includes stretching.
There's many ways to go about this. You may want to even consider looking for a book on the subject.
"i thought those were just a little harmless brown bugs, you know the ones take wings and fly? but it turned to be Flees." Fedace