Most players learn early in their table tennis lives the importance of moving opponents side to side, playing the three spots - wide backhand, wide forehand, and the opponent's middle (the transition point between forehand and backhand, usually around the playing elbow). However, a quote from a Dan Seemiller camp from many years ago has always stood out for me. He said moving an opponent in and out was even more important than moving them side to side.
The two main examples of this are:
In both of these cases you shouldn't always go short and then long; often it's better to go short a second time, catching the opponent as he moves back to react to the expected deep ball.
These types of tactics are rare at the beginning level, are used by some at the intermediate level, and are central to most advanced games. At the recent U.S. Olympic Trials, match after match had players mixing up short serve returns and attacking serves, with the server sometimes tied up trying to cover for both. Most serves were short (or half-long, i.e. second bounce near the end line), and if it was returned short, the server would either attack or sometimes drop it short again, forcing the receiver to cover for both.
Once an opponent is forced off the table, most players keep blasting the ball until they win the point. In most cases, while a short ball may set up the attack that forces the weak ball to put away, once you get that weak ball it's often better to keep attacking until you win the point. However, against a player who is returning your attacks consistently from off the table, sometimes it's better to take something off the attack to throw off the opponent's timing, and then blast the next ball. For example, if you are having trouble getting through the opponent's fishing or lobbing defense, throw in a dead block to bring him in, and then attack again with the opponent now too close to the table to defend. Dan Seemiller, both now and when he was winning his five U.S. men's singles titles, would constantly mix up strong attacks and dead blocks.
So learn to turn your opponent into a marionette, and learn to yank his strings as you move him in and out.