Schedule your audition for a time that works best for him. You want the agent you are auditioning for to be as happy and relaxed as he can possibly get so he can enjoy your audition. If he has a tight schedule, chances are that changing it around to accommodate your audition will be frustrating and hectic. You must be as flexible as you can and let him dictate when the audition will be. If he needs to reschedule, which he very well may, be prepared to throw your schedule into transition mode at a moment's notice. Have a friend at work be on stand by for you, should your audition time get changed
Provide your own accompaniment and space, if needed. If you are auditioning for an agent that wants to hear you sing, you will most likely not be auditioning in that agent's office, unless she happens to have a piano. Ask the agent from which studio she usually likes to audition people, and book a space there for you to meet. Also, provide your own accompanist for the audition. The agent will not provide that for you and she is not interested in hearing you sing a capella.
Give him a variety of material. If you are preparing monologues for the audition, prepare two or three separate pieces that are completely different from one another. If your first piece is a cutting from a modern romantic comedy, make the second piece a cutting from an Elizabethan drama. Show him that you can play different types of characters, as well. Don't put together an audition where all three characters you are playing are victims. Have a piece where you are playing a powerful character, then do a piece that shows vulnerability.
Rehearse, rehearse, rehearse. This should go without saying. Do not do a monologue or a song that you don't know by the back of your hand and can recite in your sleep. This is not the place to try out new material. Save that for open mic night. This is where you do your tried and true pieces that work every time, and that you have invested hours upon hours on in rehearsal. You cannot be prepared enough. You cannot run the pieces you are doing too many times.
Keep it short. This should also go without saying, but unfortunately even the best-intentioned auditions oftentimes run far too long. It is possible to do two monologues and a short piece of a song, or three monologues, in 3 to 5 minutes. Remember, the shorter, the better. Aim for 3 minutes while rehearsing. This gives you a little extra time once you are in the space and actually performing. Your pieces will always run longer in performance than they did in rehearsal, plain and simple. Remember that rule, cut mercilessly and you will have an audition that you can relax into once you are in the space in front of the agent.