You should have different strategies for returning deep serves and short serves. (Short serves are serves that, if given the chance, would bounce twice on the receiver's side of the table). Against short serves, you can't really loop, since the table is in the way. (You can do a backhand "banana flip," where you create a lot of topspin, though not as much as a regular loop.) So it is difficult to be too aggressive against a low, short serve. The keys against short serves are quickness, ball placement, and variation. Since your opponent has little time to react to your shot (your contact point is closer to him than against a deep serve), he is vulnerable to quick shots, wide angles, and variation (so he can't anticipate). Mix up your placement, going wide to both angles and (when returning aggressively) at the opponent's elbow (the crossover point between forehand and backhand). Mix up your shots, giving the opponent a variety of long, quick pushes, heavy pushes, short pushes, and flips at varying speeds. (Against backspin or no-spin serves, use the whole variety; against sidespin or topspin, mostly flip, but occasionally push by chopping down on the ball so that it doesn't pop up.) Whatever you do - keep opponents guessing!