OK, 11 Tips....
1) Go right up to the poker podium
Speak with the Floor Supervisor or Brush and see what Texas Hold 'Em games are running...or Omaha, Stud, or whatever poker game you want to play. Let them know that this is the first time you've been to their poker room and ask for a copy of the House Rules or at least ask if there are any house rules that you should be aware of (betting lines, posting, bad beat jackpot rules, etc.).
2) Get on the waiting list
Don't start in a big game if it's your first time playing poker in a casino or card room. Get on the list for a 2/4 or 3/6 Limit game if they're running. You'll be able to get comfortable with the flow of a poker game in a card room without risking your life savings. I wouldn't go right into a 1/2 No Limit game or a 10/20 Limit game on your first trip to the card room unless you're pretty confident.
3) Get your chips and observe the game
Get your chips from the cashier when you're waiting. You'll just have to wait for the dealer or the brush to get them for you when you get called for your seat anyway, so get them now and save a little time. Don't buy in for too much either. Take it a little slow at first and only bring "disposable" money that you can afford to play poker with. Maybe buy in for $50 or $100 if you get into a 2/4 or 3/6 Hold 'Em game.
4) Post (or wait)
When you get your seat, you can post the amount of the Big Blind to get a hand right away. Or you can wait for the Big Blind to reach your position to start playing then. I prefer to just post and start playing from almost any position, but if you want to settle into your seat and get comfortable that's fine too.
5) Always state your action clearly
When it's your turn, make sure you let everyone know exactly what you want to do. State your intentions so they don't have to be interpreted. Don't be timid, just say what you want to do loud enough so the dealer and other players can hear you. It will make things easier for you and everyone else. Stating your intentions clearly is very important. if you want to avoid disagreements and arguments.
6) Keep you cards visible and protected at all times
Concealing your cards under your hands or behind your stack of chips will lead to problems. Leave your cards in front of your stack of chips and keep a finger or two on them to protect them from being mucked and killed accidentally. You can put a trinket or a chip on top of your cards, but the absolute best way to protect them is to have them under your fingers (I'm not a big fan of trinkets, medallions, rocks, miniature statues, etc. being used as "card protectors"). Also, don't remove your cards from the table, take them out of view of the dealer or drop them on the floor.
7) Keep your chips in neat stacks - 20 chips high.
This is just normal for most players. It'll make betting easier and makes it easy to tell how much you have in front of you. You could just have a mound of chips of assorted values in a big pile in front of you, but that's just bad poker etiquette.
8) Follow the action and pay attention
It's so frustrating when a poker player has to be told repeatedly by the dealer or other players that it's his turn to act, how much the bet is, or who raised. Be social, of course, but also follow the action and know what's going on. Plus, when you know where the action is you are actually protecting your own action, which is a whole other discussion..
9) Hold onto your cards until the pot is pushed toward you
When you win a pot, MAKE SURE that the pot is being pushed to you before giving up your cards. This will make sure that your hand won and that there is no disagreement about who won and who gets the pot.
10) Take your time at the table
Be deliberate and think about what you are doing, and do what you feel is best. Don't let the other poker players influence how you play. Everyone plays poker a little differently, so find your own style and go with it. Don't let the table coach intimidate or embarrass you...he's typically full of it and just embarrassing himself anyway.
11) Have fun!
Socialize with the other players and have a good time! If playing poker was a drag who would do it in the first place?