How do you get maximum power on your shots? Many players at the beginning/intermediate levels might say "swing hard!" But that's the worst thing you can do. Until your muscles are trained properly, swinging hard means spastically using a few muscles but not all of them. It also means putting less weight into the shot. Both cases result in either wimpy shots that any well-trained kid would laugh at, or sometimes powerful shots with no control.
Watch a baseball pitcher with a good fastball. (You can find many at Youtube.com) Many of them can break 100mph, and nearly all are in the 90s. Watch these flamethrowers; are they swinging hard, or are they swinging smart? I think you can see the answer; the most powerful throwers don't seem to put full effort into their pitch; in fact, their throws seem effortless. And they're able to hit a rather small target from over 60 feet away.
Now watch the top table tennis players, and you'll see the same. The shots of the most powerful players often seem effortless. Meanwhile, watch some intermediate players as they swing as hard as they can, usually with less power and always with less consistency. Many spastically use one or two muscles at full power while losing the power of everything else, including their body weight rotating into the shot. Their shots spray all over the court as you cannot control a muscle spastically contracting at full power.
A key here is that these baseball pitchers and table tennis players not only have power, but they have control. How do they do it? The secret is they use their full bodies in a fluid motion that rotates everything smoothly into the shot, leading to power and control. It starts from the legs, then the hips, then the waist, then the shoulders, then the arm, and finally the wrist, which effortlessly snaps into the ball like the tip of a whip. All these muscles are engaged as the player accelerates into the shot, creating the seemingly effortless power of a pitcher or top table tennis player.
It is the addition of all these smooth muscle contractions and rotations, in the proper sequence (from bottom to top, and roughly from big muscles to small) that gives great power and control. So here's a good rule: never swing at 100%. Swing smoothly, using the full body, at perhaps 70-80% full power, and watch the power and control shot way up.