If you're interested in playing (or have just started playing) Texas Hold 'em Poker, there's dozens and dozens of books and sites that will tell you how to play your hand, what to look for, where to play, and so on and so forth. Nearly all of them skip one of the most important aspects of a real-life game - how to physically play the game.
Of course, none of this applies if you are playing on-line - you might as well play naked and yell 'Jackpot!" everytime you get a pat hand. However, if you are playing in a real casino, the way that you physically play has an effect, both on yourself and the competitors around you. You want to maximize your advantage every way you can and this is a list that will tell you how.
A caveat: all the physical prep in the world won't help a player who calls on a 10-6 unsuited, if you know what I mean. Study up.
It's a terrible mistake to classify players based upon what they are wearing. However, there are times where you can pick up some subtle hints from their appearance. So we'd like to be the ones picking things up and not giving anything out.
Dress casually, but cleanly. Muted colors, nothing that draws attention to yourself. (Let your playing do that.) The pros can wear shark skin vests and cowboy hats, you can stick to plain t-shirts. Don't bother wearing sunglasses, you'll look like a poseur, a Celebrity Poker wannabe. Don't kid yourself about how advanced your game is.
Your clothes have to be comfortable for sitting - you're going to be spending more than a few hours seated in the same chair. If you're distracted by the belt of your pants digging into your waist, you're not going to be paying enough attention.
Oh, man, you'd think this one is obvious. Do not drink alcohol while playing poker. There is not a single advantage to drinking while playing, unless your goal is to enrich the other players. If you start getting even a little reckless while playing, your chips will suffer. Staying in too long, missing signals, forgetting your turn - all these things will drain your money, sometimes quickly.
Conversely, watch to see what everyone else is drinking. If someone is knocking back a few cold ones, prepare to feast on their chips.
The cards are random. In the long run, everyone, drunk or sober, rich or poor, will get the same number of good hands. Those that have lost most of their money are doing something incorrectly, something that is transferring their money to someone else. You need to find out what that is, both to help you take money from them and to prevent it from happening to yourself.
Do they have an obvious tell? Are they 'chasing'? (Staying in bad hands hoping for a straight or a flush.) Tilting? Drunk? If you can figure out what it is, you've got a leg up on them. Don't waste too much time studying the good players in your game, you get just as much money taking $10 from ten suckers as you would taking $100 from Phil Helmuth.
If you're tired, distracted, or just plain losing, quit. Cash in your chips and go home. You can always come back tomorrow. When you're not playing at your peak, you're throwing your money away. (Either directly or by not winning as much as you could've.) Worse yet, someone might figure you out and start making some easy withdrawals from the Bank of You-ville.
Don't let it happen. Color up, check out, get some fresh air and some sleep. Let your money accrue a little interested until next time and you'll be a richer person the next time you walk in the door.