As with any tennis practice the ability of the persons involved dictate whether or not that said practice will work and will be beneficial.
There is nothing as bad as a bad practice!
So the ideas I set out in this section will start with very basic practices that two people can do.Obviously it is advisable to have an idea of the technique involved in each practice and try to maintain it.
As you are hopefully working with a friend the two of you can help each other by commenting on any errors you see your partner making-be constructive and not critical.
It is often easier for someone else to see your errors.

So the first practice is the good old mini tennis where the two of you are trying your hardest to keep the ball going between you using the boxes only.

This is a a multi stage practice;

1) Try using your forehand/backhand drives only, working on your SHORT backswing but with the full follow through.The use of top spin is beneficial in this practice.Hit at a speed where the two of you can control the rally.

2) Use volleys to each other.A great practice to get you happy playing from this mid court postion.Where of course, when you get better, you will want to be when approaching the net.Try to keep the ball LOW but if one of you plays a high ball just then volley back to the feet of your partner so they can reply with a low volley.If the ball bounces short play a drive back to your partner.

3) Bring in a half volley, DO NOT GO OUTSIDE THE SERVICE BOXES.

4) Anything goes,drive,half volley or volley, you decide, and thats sometimes the problem, making the right decision.But after a while you can really improve your mid court game and work on that so important part of your game CONTROL.

5) Finally move each other away from the middle of the boxes using the width, working on lateral movement, BUT AT A PACE THAT BOTH OF YOU CAN MAINTAIN THE BALL IN PLAY.You can still use any shot, a great practice for trying that difficult "volley on the move" and of course the recovery steps.

Play this everytime you get out to practice.I would suggest 5 minutes on each stage, and if possible try to make the last stage last 20-30 strokes.