Figure out why you are nervous. Are you afraid to get a bad grade? Do you think you may embarrass yourself in front of the cute guy in the first row? Once you identify these thoughts, begin to find reasons why they won't be true. For example, when you think, "I am going to make a fool out of myself in front of Brendan.", think something more positive such as, "I am going to be so prepared, I will sound really smart and Brendan will be really impressed." Obviously, your thoughts and examples should be specific to you.