You must be prepared for the auditions process as if your life depended on it. In fact, it does. The auditions process is what separates would-be actors from real actors. Real actors treat their talent like an art form, and they take it seriously. This means that they treat the auditions process seriously too, because they know it will be the difference between getting the part and crying into their latte about not getting the part.
How can you ace the auditions process and nail that next appearance? First of all, work on your chops and have an arsenal of actor's weapons at your command. Voices, monologues, poems, easily accessible emotional responses you can slip into to deepen a short performance, all of these things not only improve your performance, but they help break up the monotony of the auditions process for everyone else involved, who may have seen a lot of the same thing over and over all day.
This, in fact, is the key. The auditions process is long and methodical, and your job is to make them remember you. It is important to keep this in mind. You might mess up your lines, you might feel awkward, but if you blow them away with a deeply felt emotion, or crack them up with a funny voice or character, you have conquered the biggest obstacle for actors in the auditions process.