Many times, in doubles I teach my students some basic patterns of play. In doubles, when you are at the net and you receive a low ball (a ball below your waist), what should you do with it?
 
If your opponents are both at the net keep it low down the middle. They will have to fight for the ball and will be unable to add too much angle.
 
If your opponents are up and back, return the ball to the opponent the farthest away from you.
 
When both your opponents are both back, return the ball to the opponent farthest away from you. Then both you and your partner need to back up and look for an overhead.
 
If the ball you hit to the deep player falls short, both you and your partner should move in to lessen the chance of your opponents hitting the ball low and under you. Most players do not lob moving forward.
 
Remember, if you receive a low ball at the net return it to the farthest player from you then look for a lob. If you hit the low ball back short to the deep player, move in. What are considered low balls? Low soft volleys, low fast volleys and low half volleys.
 
Good luck on the courts!