First for fun! Even if the game is about money, never consider it more than just an addition. If youre scared of losing money you shouldnt be playing.
NOW NEXT - KEEP that feeling of losing and understand that you are not out of your mind for being right. Eventhough the game is about betting like the song says "You gotta know when to hold'em and know when to fold'em." If you dont have the cards ITS WORTHLESS!
Facial expressions and hand gestures dont do anything but tell you the player is excited. It could be for a number of reasons. Look for only how he or she reacts when you are deciding your move.
NEXT - IF YOU ARE RIGHT YOU ARE RIGHT. In many decent non overpowering hands like 2 pair or a high pair like 2 Aces, there is a possibility of a better hand and you dont feel that throughout your play up until this point that it is worth it......ITS NOT.
Thats it.....GO HAVE FUN!...and win.