Your Serve, My Serve

This activity from Cosmin Milhoca is similar to Tina Hoskins' Serve Everlasting drill. Here it is verbatim from Cosmin's website, Web Tennis Drills:

Your Serve, My Serve

Two players (A and B) play a game where each point starts with a serve from behind the baseline.
One of them serves - let's say, player A. She is going to keep serving, alternating sides after each point, until her serve is broken (that means she loses a point on her serve).
Once that happens, player B will begin serving - first point from the right (second from the left and so on). Now, player B will continue serving on each point until her serve is broken.
Scoring: Every time a player serves and wins a point, they count it; players don't get points for breaking their opponent's serve. Play first to 11 (counting only the points won while serving).