Make sure that everyone can hear you. If your auditions are in an actual theater, great! But since they are usually not, make sure you talk as loud as if you were in a theater and the directors were in the back row. Don't push it though. Make sure it still sounds very natural, and not like you're screaming. If the directors can't hear you, they won't give you a good role because no one in the audience will hear you! Stage microphones only pick up sound that is loud enough!