[smarterthanyoda]

The best way to avoid giving tells is to learn how to spot them in other people and then avoid doing those same things yourself.

Study some of the literature about body language and expressions. ("Emotions Revealed," by Paul Ekman is a good start.) Once you understand the distinct movements that give tells, start practicing them in a mirror. When I tried that myself, I started recognizing the same movements when they came subconsciously.

Larry Phillips recommends putting a mirror next to your computer screen and watching yourself as you play a computer poker game, like "Poker Academy Pro." This never worked for me just because I didn't feel any kind of stake in the computer game.

Of course, this is assuming you're already aware of the types of broad tells like "Weak Means Strong." If you're looking for that level of tell, the best source I've seen is still "Caro's Book of Tells."