Summarize this article in one sentence.
. Curves can be hard, but once mastered; they can save your game. Here's a few things to keep in mind:  Watch the angle of your opponent's racket. If it's moving from low to high, you can expect topspin (spins upward). From high to low, backspin (spins downward). From left to right, ride sidespin, and from right to left, left sidespin. You can compensate for spin with your racket angle. If you're facing a ball with topspin, angle your racket down and hit to ball above its center. If you're facing a ball with backspin, angle the racket up and hit the ball below its center. If right sidespin, angle the racket to the right and hit the ball on the left. If left, angle the racket to the left and hit the ball on the right. Master the art of the sidespin, too. This can severely limit your opponent's options when it comes to returning the ball. Experiment with hitting the ball on the right or left and drawing it to center, creating a sidespin. Often the ball won't go where your opponent expects it to go. Your whole body is what gives you power – not just your arm or wrist. You need to swift and agile, using your hips and shoulders, too. To stroke your forehand, rotate your hips and shoulders backwards during the backswing. Then come forward as you complete the swing. This transfer of body weight gives your swing more power and oomph. If also leads to a consistent attack. Even if you don't have your technique down 100%, if you play like a madman with no consistency, you'll be able to psych your opponent out. Go deep, go short, use spin, hit it straight, go pure speed, ride the ledge, etc. Keep the competition on its toes. To make this easier on you, use that ready stance. Be ready to transfer your weight at any point, but especially after serves and in between strokes. Be ready for an attack at any given moment. Remember that the ball weighs almost nothing. It's always spinning, too. If you come at it with a tight grip and with hard, stiff force, you're going to kill it in mid-air. Before you get into a game, loosen up your body and your grip. It just needs a light touch, whether the ball comes to you or whether you have to go chasing after it. Relax your mind, too. If you lose control of your temper, you might as well hand over the game. If you've missed several shots in a row, don't get mad – get even. Never give up until the game is over. In ping pong, the tide can turn in a heartbeat.

Summary:
Curve or add spin to the ball Use your whole body, especially when you stroke your forehand. Mix up your length and speed. Relax your body.