I was originally going to post this as an addendum to Fro's advice for Beavis from yesterday, but now that I think about it, it's probably more suited to someone who has a little experience and wants to get better, rather than a true novice. First of all, the unfortunate truth: Tells are not nearly as important as movies might have you think. They are great for Hollywood drama and they can help you make an extra bit of money every now and then, but unless you understand the game extremely well, all of the mistakes you are making will quickly cause you to lose money at a rate much faster than any tell will win you money. Similarly, tells are not always reliable and thus should likely be a tool you use in addition to sound poker logic. You should never make a play solely on the basis that you might have noticed a tell in another player - it's just too risky.
The other piece of reality surrounding tells is that they are not as dramatic or as individualistic as Hollywood might have you believe, either. Occasionally, you might find one in specific a player that is very unique and very reliable, but that will only come if you play cards often with that person and have lots of experience from which to gleen your conclusions. Generally, though, the most commonly known tells are quite generic. For a specific listing of these generic tells, go buy yourself a copy of Mike Caro's book, because I'm only going to discuss one that I think it very powerful, especially for new players, which is the act of looking at one's cards.
Quite simply, you should always memorize your hole cards. Look at them one time, maybe for a couple of seconds, then don't look at them again, because every time you do you are possibly giving away your hand. A three-flush flops in holdem? Most players instinctively look at their cards to see if they have one of those cards in that suit. Players who don't look probably already have two cards of that suit, or they have two cards of a different suit, and don't have to bother looking because they already know what's under there. Similarly, if a face card or an ace flops in multiple suits and a player looks at his cards, he likely has one of those and is now checking to see if his kicker paired up. That is, he noticed right away that he paired the big card, but he's not sure about the other card and he wants to make sure. No matter the circumstances of the hand, once you can draw a conclusion as to why a certain player looked at his cards, you can combine that conclusion with other evidence you might have about his hand to try and come up with a better read of his cards. It's another piece of the puzzle.
This may seem extremely simple to you and that's because it is - but as a matter of trying to find an edge against other players, every time you look you possibly give an advanced player more information towards figuring out your hand, be it from your actions after looking, your facial expressions while looking, or the length of time you look while you spend extra milliseconds trying to differentiate between Aces and Fours and Clubs and Spades. If you make an effort to memorize them, it's not hard to do it whenever you see it for the first time - even in Omaha - but the trick is making an effort to do it in the first place. Memorize them one time and don't look again - they're not going to change.
Random thoughts from a lawyer, an accountant, a commodities trader, an ex-Marine and a WSOP Main Event money finisher that don't know as much as they wish they did...