Joe Navarro ftw, imo.
My favorite "tell" anecdote happened during the wsop last year. I'm very talkative at the table and usually pretty friendly, I think this really helps pick up tells on people because once you're friendly with the other players it seems that they become more honest with you.
So a guy (middle age white dude wearing a cap) raises to 600 with like 8k behind at 100/200 25 I think, and it folded to me in the BB with 22. I call and the flop is K83r I check and the guy checks, the turn is an Ad putting two d's on board. I decided to bet at it because I felt that it was more likely that he had 99 -QQ than Ax so I bet about 1,200. He looks back at his cards, grabs chips to raise shuffles for a little and then just calls. The river is another 3x.
I thought about betting but by now I decided he either has AT-AQ or he has a flush draw that missed. So I check and he grabbed like 4k which was more than half his stack and about a pot sized bet, and he throws his chips in with a flick of the wrist, giving the chips that kind of "spin" throw... I don't know if this is how he value bets or if this is how he bluffs but I decided to stand up from my chair and yell "YOU DID THE SPIN THROW, THATS ALWAYS A BLUFF" just to see what his reaction was, he remained just as still and quiet. At this point I knew that if I talk for 2 minutes I'd eventually be able to get one or two tells that will let me decide whether or not I can call. So for the next 2 or 3 minutes I kept saying stuff like "I cant beat anything, but I can probably beat you" "I make one sick call per tourney, this might be it" etc etc....this guy wasn't giving anything away, and finally I decide to go under the table and look at his feet. Navarro says the feet are the most truthful part of the body and whenever I look under the table people always think I'm just being a clown and they don't change the way their feet are positioned. So I go under and see his feet are flat on the ground, I come back up and I say "your feet say you're bluffing" at which point he smiles at me, I throw the chips in and he mucks his hand, I show the 22 and the guy announces to the table "You know what the sick thing is.....I've seen him do this before"

pretty sure I didn't get bluffed again at that table.
Anyway I talked about this in the gobbo thread, I think the best advice I can give for reading people is to wait for 2 or 3 minutes before you decide anything. You should also usually look for 2 or more tells before you're convinced one way or the other, in this case it was the way he threw his chips in + his feet + his smile. When they have a strong hand, especially with fish, it's way easier to get 3 strength tells, like he breathes heavily, his eyes are looking away from the table, and 3 minutes later he puts his hands behind his head. From my experience there is almost always a huge tell after a 2 minute stare down.
Also, I had a lot of trouble focusing on people at the table and learning their tells when I first moved from online to live. A friend of mine who is a live player gave me a good tip/exercise to try at the table so I could get used to picking up physical tells. What he told me to do was to forget everyone at the table and just pick one guy every hour, and focus on everything that guy does, soon enough you'll get into the habit of looking at all of the players at your table at the same time, and you'll pick up something on almost everyone.
Hope that helped a little.