Simple etiquette is actually quite important at a poker table, although the atmosphere is usually pretty laid back. I'll try to walk you through your first experience at a poker cash table in a casino.

First and foremost, you should get acquainted with your surroundings. Casinos can be huge, especially in Las Vegas! Make sure you know where to buy chips, cash out, and check out the different poker tables and decide which type of game you'd like to try out first. I'm not sure how familiar with poker you are, but if you would feel comfortable, stand near a table and observe for a while. See what people are doing and how they're acting. You will most likely see a mix of both intense moments surrounded by silence, and casual chatter or table talk going on. Anything is completely appropriate, as long as you are not swearing, yelling, excessively celebrating, or doing anything else to cause a scene.

As soon as you feel ready to sit down, you will go to a counter nearby to buy poker chips. Sometimes you can get them at the table, but in my experience, I have always gotten them at a station. Now, once you have your chips, you will find an open seat and sit down. If you are not sitting in the big blind, you will have to post if you would like to start playing right away. This means, you will place a bet of the big blind, no matter where you're sitting, just to make sure there's money from you in the pot. You always have the option, however, of waiting until the big blind reaches you. This sometimes takes a while though.

Other than this, you're all set to go! The etiquette at the table is just what I mentioned before: no making a scene, and they normally don't allow swearing, at any volume level. What to expect... well, you never know what to expect at a poker table. I would suggest that you don't set high expectations for winning a lot of money. Start out on low blind or betting levels and see what happens. Make sure you wait your turn before folding or placing a bet. Don't insult anyone verbally. Also, make sure to announce your action before you do it. For example, instead of just throwing a $5 chip out with the intention of raising $3, if the blinds are $1 and $2, you must say "raise" just to make sure your betting action is clear to those around you. If you don't do this, you might get called out. Nothing terrible will happen, the house might just rule that the bet doesn't count. All verbal actions are binding, so if you say "all in," you better mean it!

Really though, as I said before, the atmosphere in the poker rooms at casinos is normally very casual and laid back. I expect you'll have a great time. Keep all these things in your mind during your first casino poker experience, but don't let these "rules" overwhelm you. Try to have fun!! I wish you great luck and winnings on your 21st birthday, and I hope you enjoy poker as much as I do!

You might see this, you never know with poker!:
http://www.energizedevents.com/assets/ee-images/product_casino_poker_table.jpg

There are several tips on how to have good etiquette when playing poker at a casino. Following them will keep you in good grace with the other players.
1. The first one is to avoid string bets. This simply means that you need to announce the word “raise” and then you can make as many trips to your chip stacks as you need for more. This prevents players from putting money out to check out the reaction of the other players and then going back for more.
2. While you are still in your hand, do not discuss it trying to get a reaction from the other players.
3. Always treat the dealer with respect. Remember they had nothing to do with it if your cards turn out to be bad.
4. Pay attention to the game so you don’t hold it up. This includes talking on your cell phone or chatting with others behind you. Do take time to make your decision.
5. Do not ever remove your cards from the table.
6. When it is time to show your cards, be sure to show both of them.
7. Don’t talk about the hand when you’re not in it, or give away the cards you folded.
8. Don’t throw your chips in the middle because it can confuse the dealer.
9. Don’t show your hand to other players.
10. Do not fold your hand until it is your turn.
11. Don’t tie up a seat when you have no intention of returning.
12. Don’t be rude or obnoxious to other players.
13. Follow other rules of good conduct that you would when not playing poker.

Remember poker is a good, so relax and have fun!