Improve the accuracy of the players deep forehand cross-court.
Set up the targets with line markers in each deep corner of each player. Set the size of these targets according to the players level. It can be frustrating for players with lower level if they constantly miss.
In this example one of the players is feeding the first ball, in this case if he hits the target on the feed, it does not count. There is, of course the option that the coach feeds the first ball.
As the drill says, it is a competition. In the video, the first player to hit the target 11 times wins. You may play less, or more.
You can make it a little harder, by deducting the points should a player hit the ball out or into the net.
For higher levels you even may make a difference if a player hits the ball out or into the net (i.e. Out: -1 point and Net: -2 points).