Firstly one pair starts on the baseline, the other half way inside the service boxes. Coach stands on the baseline behind the net pair and feeds a ball to the baseline team.  The baseline team have to practice passing shots, NO LOBS!  The net pair "must volley!" Any ball that the volley teams lets bounce is a point to the baseline side. The idea is for the baseline pair to beat the net pair 5 times. In that time the net pair should count every pointthey winas well. Once the net team have been beaten 5 times they switch roles with the other team.

Coach... when feeding, alternate to the baseline team. First to the left players forehand, next feed right players forehand, then following feeds to the backhands. The main idea is to practice low returns using the width of the doubles court. The net pair needs to volley either deep down the self, or try to volley short. If you have really good players you can add that the net pair must volley outside the opponents service boxes. (ie any volley short is a lost point to the net team.)

Another variation is that after the first volley the baseliners can lob, and the net players must take everything out the air, all the time and that's difficult.