I do sprints and a little jogging a couple times a week as well as some leg strength exercises and stretching.
Here's the thing I do that is a bit unusual.
Once or twice a week, I do some "mini-hitting" and hand-eye coordination work. Right there in the living room I can hit the ball with full-knee-bend, against an area of wall 3 feet wide and from floor to ceiling. I stand back about 6 feet from the wall and use an old wood jack kramer staff and a ball (wood floors). You have to have a very soft touch and some serious movement to keep that ball under control. I can hit almost as well lefty as righty. Then I do some close control work with just the racquet and the ball. Tossing and catching the ball without letting it bounce on the strings etc. The heavy racquet makes it an awesome workout through the wrists and forearms.
Of course, table tennis is always nice too.
Pushups, sit-ups too.