Encourage the server to focus more on doing good serves, as he has a limited area to play to after his serve.
You can set up this drill by simply extending the center service line to the baseline with line markers. It is always the server who has the limited area to play to.
As you see in the video, the server is only allowed to play to the side wherever he has served to, forcing him to perform good serves in order to have a chance to win his own service game.
You may play normal games for this drill, as well as t-breaks if you like.
To give the server a bit more space to play to, you may include the doubles court for him.