Playing poker in a casino you have to act courteously, remember you are not alone at the table. The best rule is "Do onto others as you would have them do onto you."
Before playing in a new cardroom, read the house rules. Most casinos have the same general rules, but some vary them. Make sure you know the rules of the game before you sit down.
Poker is a game of information. It is important that you don't give information that would help others. The first rule is, wait until it is your turn to act. If you act out of turn, say through away your cards before it's your turn, you are giving valuable information to players who have yet to act. To prevent prematurely giving away what you are going to do, wait until it's your turn to act before looking at your cards. This also helps you by preventing you from giving away the strength of your hand while others who will act before you have decided what to do.
All casinos have a rule, "One person to a hand." Never discuss a hand while it is in progress or give advice to an active player. The later will earn a rebuke from the dealer or a formal warning from the floor man. If you persist in advising active players, you will be banned from the card room.
If you are going to raise, say "raise" when it's your turn before doing anything. The rule is you have to say either raise or place all the chips in the pot in one motion. Saying "I call your bet" placing the bet into the pot, the "and raise you" then placing more chips in the pot is called a string bet. This is not allowed. A cheat could say "I call" look at his opponent's reaction then decide if he wants to raise. Cheats are known as "Cross roaders" and the action is called a "Move." Casino's don't want cheating because it drives honest players to the competition.
Try and keep the game fun and lively, especially at low limits. Most players are there to have fun. Helping keeps the game fun keep's recreational players, who usually are bad players, in the game increases your chance to show a profit. Never, never, never, berate a bad player. There will be occasions when you are a huge favorite to win the hand, but a bad player calls your bet, catches a miracle card and beats you. You have suffered a 'bad beat' and you will be tempted to tell you opponent how bad a player he is, insult his mother, and launch into a tirade of invective. You see this happen often. Don't do it. Not only is it rude, it is bad for your chances of making a profit. Poker is a zero sum game. If you win, someone has to loose. Losers are usually the bad players who are playing for fun. You want these ‘fish' to stay and play as long as possible. Remember P.T Barnum's motto, "Never give a sucker an even break, and never wise up a chump." If you anger a bad player, he is likely to pick up his chips and go home. Veterans have a saying "Never tap on the aquarium." You may feel friendly and try and give advice to a bad player. Curb your ego. Bad players don't want advice and resent someone pointing out how badly they play. Remember never wise up a chump, that bad player is where you will find your profit. If you do succeed in improving his game, you are diminishing your winnings. If you have to say something, complement the player. Tell him what a good play he just made, or say you never would have the courage to do what he did. Pump up his ego, he will stay and pump up your winnings.
To sum it up. Follow the rules. Be a friendly courteous player. And "Don't tap the aquarium."