Select the right game for your skill level and pocket: Don't jump into a game with higher stakes just because you just won an easier one. It's better to be the best player at an easier table than the loser at the harder one.
Don't play when you are emotional: You won't play your best if you play "on tilt" -- playing emotionally, not rationally. If you lose your cool during a game, take time out to calm down -- otherwise, you risk having other players pick up on your state of mind and take advantage of you.
Be willing to fold more often: Don't feel like you have to play every hand - you will only lose more this way. If you are dealt a poor hand, don't stick with it hoping to improve it. If you are obviously beaten, be willing to part ways with your hand, no matter how good it was when it was dealt, or how much money you've put into the pot.
Pay attention to the other players: Watch other players, even if you've already folded. Watch for patterns, player reactions, and body language. File this information in your mind and use it when you need it.
Don't assume that playing at the casino is just like playing online: At the casino, you'll have to play more wisely against possibly more skilled players. Also, your body language and tells are now on display for all to see, which is not as easy to figure out online.
Bluff wisely and sparingly: Don't bluff just for the sake of bluffing. Don't use it as a way to get yourself out of folding all the time. Fold if you have to -- bluff occasionally.
Don't raise unless you think you can call a re-raise: There is always a chance of being re-raised, so make sure you are prepared to do so in case it does happen.
Don't call unless you think you can raise: When someone else bets, play the hand if you think you might have the best one, and you want to make others pay to draw out on you.
Be a humble winner and a graceful loser: No one likes to play with a show-off, or a sore loser. Maintain a good attitude, and have fun.