This is one of the drills that are just great to begin the tennis practice by warming up the body and getting a good feel for the racquet–ball control.
Both players are positioned behind the service line, on opposite sides. (see graphic below)
In the beginning, they rally cross-court (1) trying to keep the ball only inside the deuce service box; then (after about a minute) they rally cross-court (2) keeping the ball only inside the ad service box; followed by the down-the-line rally (3) then down-the-line (4).
Hit the ball at a slow pace by shortening the backswing, keeping the feet moving at all times.
After the two players do this drill for about 4-5 minutes they can move further back and hit the ball deeper and harder.