A great way to warm up your doubles game with four people on one court is to have one team dink straight ahead while the other team dinks cross court. This gets everyone involved with one ball. After a while, you simply switch. This simple drill is an effective way for all four players to get ready to play while working on both straight ahead and cross court dinks. If there is enough time in the warm up session, players can also switch sides with their partner in order to get reps hitting both right-to-left and left-to-right cross court dinks.
To maximize the effectiveness of this drill, focus on proper positioning as well as touch and placement of your shots. Work on staying in a low, athletic position with your knees bent and moving your feet so you are in the proper position every time, no matter where the ball is hit. If the ball is hit a bit longer, take as many quick steps back as needed to be able to keep the ball in front of you (instead of standing still and hitting the ball at your feet or slightly behind you). Similarly, if the ball is hit away from you, move quickly to get yourself in good position before the ball lands (instead of making minimal movements and lunging or extending too far while hitting your shot). Not only does this work on proper mechanics and shot execution, it also gets your body warm and ready to play.