I've read a couple of books on tells
and have tried to incorperate them into every game that I play in. Of all of the ones I've read about, the only two that seem to be pretty much universal are as follows.
1: When the obnoxious guy shuts his mouth. Usually, when someone is talking constantly throughout the game (especially to someone who is not playing), then instantly shuts up for a few seconds after looking at his cards, they have a strong hand.
2: Look at everyone's posture when you start playing. I try to ignore facial expressions or eye directions (at least untill I get better at reading people). For the most part, no one pays attention to their posture and rarely fake it. If someone has been slouching in their chair for the last 10 hands then sits up straight or has been sitting up straight and leans foward a little, they are usually pretty strong.
These are the only ones I've been able to use effectively. There are thousands of others that have to be applied to specific people at specific times (looking at chips immeadiately after cards, prettending to look of into the distance, covering their cards with their hands even when laid face down on the table, ect.) but I'm not so good at using them so I would feel sheepish sharing. The best book I've found for this is Mike Caro's book of poker tells.