1) Don’t Play Out of Turn
While you may be so excited about how good your hand is you can hardly wait to raise the pot, you have to wait until it's your turn to do so. Same goes for folding hands you can't wait to get away from. If you jump the gun, it gives other players information they shouldn't have before they make their own decision and can confuse the action.
2) Don't Talk About Your Cards While the Hand is Still Going On
Once you've folded, it's tempting to chat about what would have happened if you had stayed in, but if anyone who's still in the hand hears, it'll give them information that they might use to their advantage. For instance, if you had a 7-2 as your pocket cards in Hold'em and the flop comes 7-7-2, if you blurt out that you would have had a full house, everyone will know that it's unlikely that any player still in the hand has the full house, making it hard to bluff and represent that hand.
3) Don't Show Your Cards (Until the Showdown)
When you fold, make sure you don't flash or flip over your cards as you toss them into the muck. Again, if players know what you fold, it'll give them information that may change how the rest of the hand plays out. Unless you are all-in and heads up, there is no reason to show or expose your cards until the showdown.
4) Don't Splash the Pot
There are two bad betting habits that you see a lot in the movies which are no-nos in real life. The first is when a player tosses his bet in a big mess in the center of the pot. That's called Splashing the Pot, and it makes it hard to tell how much you've bet. A better way is just to stack your chips neatly in front of you to bet.
5) Don't Make String Bets
The second bad habit from movies is the string bet, which is when a player goes "I'll call your 500.... and raise another 1000!" You have to declare whether you're simply calling or raising right away -- once you say "call," that's all you can do. If you're going to raise, say raise and the amount right away. This is especially important in casinos.
6) Don't Be Rude or Mean
Even if you're having a bad losing streak, it doesn't give you the right to curse other players or be rude to the dealer. It will win you neither pots nor friends.
7) If You Show One, Show All
If you win a hand before the showdown but want to show your cards anyway, you can't just show them to the one player to your left or right, you have to turn them up for the whole table to see. After all, why should only the lucky players next to you get to know what you were holding?
8) Do Pay Attention
If you're in a hand, don't make everyone remind you that it's your turn -- keep up with the action so the game keeps moving. Talking on cell phones is a bad idea.