When you begin to learn poker, you naturally start with the purely mechanical aspects of the game. It is crucial to remember, however, that in a game whose basic structure relies so much upon chance, the skill involved to play is just as much in the manipulation of expression and words as it is in the manipulation of cards. Poker is a game of shadowy diplomacy, of royal court intrigue. Your appearance, your poise, your mannerisms, will cause your ascension or ruin just as often as the five cards out of which you try to construct your ladder to the top of the game.
When you are truly conscious of yourself, you can exercise far more control over your appearance. Try to bring this awareness of yourself up when you play the game. It might help to start by playing online poker, when opponents can’t see you, so that you can focus fully on yourself. It also can be of great benefit to have someone watch you. Get to know your ticks and movements, and get to the point where you can prevent or manipulate them as you see fit.
When entering an actual poker tournament, there are three basic tactics you can employ in regard to tells. First, you can adopt the classic, stony ‘poker face.’ You maintain a constant neutral expression, attempting to give nothing away at any time. The advantage of the poker face is that it is the hardest tactic to try to read. There is nothing to interpret or pick up. The disadvantage to this tactic is that if you let the wall crack even a little bit, whatever you do will stand out sharply. Second, you can act slightly more ‘naturally,’ smiling, laughing, frowning, running the gamut of expression within a limited framework, as long as you avoid adopting particular manners at specific times. This is hard to read, but in trying to be naturalistic your instinctive tells may shine through at times. Third, you can attempt to intentionally mislead your opponents by employing false tells to throw them off. This can grant you big short-term gains. The disadvantage is that it will only work a few times before any given opponent recognizes the deception.
Sun Tzu said, know yourself and your opponent and you will win 100 battles before losing even a single poker game. First and foremost, know yourself. This is the key. 
