Here are the basic rules (given by the ITTF) that you may or may not have known about playing table tennis, and some of the myths that people are still abiding by. This is not a complete set of rules, but simply an explanation of the rules most often broken.

1. Games (or Sets) up to 11 Points, 2 Serves each.

   Before 2000, games were played up to 21 points, and each player served 5 times in a row. The game has changed and now each set is played up to 11 points, and each player serves twice before switching.

2. Serve: You cannot hide the ball as you are serving.

   After tossing the ball up for a serve, many players still leave their other arm out, covering the opponent's view of the ball during service. This allows the server to use different spins and trick the opponent, and with the contact point covered up it becomes incredibly hard to properly return these serves. This used to be allowed before the year 2000, but a rule change has since been put in place to make it easier for the receiver to see the service clearly.
   
   You must remove your arm so the opponent can clearly see the contact point of the serve.
   
   

   Illegal Serve Notice the serves labelled "Unclear", Ma Lin covers the contact point with his arm.

   Legal Serve Werner Schlager's serves are never hidden from the receiver's view.

3. Serve: You must toss the ball at least 16cm.

   A lot of players don't toss high enough, or simply don't toss at all and simply let go of the ball and hit it immediately. You must toss the ball at least 16cm, then hit the ball on the way down (not on the way up!).

4. Serve: Toss the Ball Vertically.

   You must toss the ball nearly vertically, within a few degrees. You cannot toss it at a sharp angle (like diagonally at 45°). Sharp-angled tosses make it easier for the server to put extra spin on the ball.

5. Serving in Doubles: Serve from Right-to-Left

   In a Doubles match, serving always happens from the right half of the table (from the eyes of the player who is serving) and must go to the opposite diagonal side. Never will you serve from the left half of the table. If the ball doesn't bounce in the proper halves, the receiver's team wins the point.
   
   In Singles games, the server can serve from anywhere to anywhere.

6. Serving Distance (Myth)

   There is no rule on how far the ball must go when you serve. The serve must simply bounce once on the server's side of the table, and then bounce on the receiver's side. Some players believe that the serve must go further, so the ball does NOT bounce twice on the receiver's side, but this is a myth. Professional players routinely serve very short so it will bounce on the receiver's side many times before falling off the table. And likewise they also serve very long balls that will only bounce once on the receiver's side.
   
   Also, the ball is allowed to fall off the side of the table. Essentially, as long as the toss is legal, and the ball bounces once on the server's side and at least once on the opponent's side, then it's a legal serve.

7. Hitting the Ball with your Hand

   You are allowed to hit the ball with your racket-holding hand and the handle of the racket, as long as that hand is holding the racket. So you can purposely or accidentally hit the ball with the back of your hand, and it would be legal. But if you drop the racket or throw it, you cannot play it at all. So throwing your racket at a ball will be illegal since you are no longer holding the racket.

8. Touching and Moving the Table

   If you touch the surface of the table with your "free hand" (the one not holding the racket), the opponent wins the point. Touching the table with your racket-hand is okay.
   
   If you move the table, you lose the point. So if you bump into it and it noticeably shakes or rolls (if on wheels), then you automatically lose the point.