Know What Your Client Wants — What you should know.
It is my core belief that if you do not have a firm grasp of the needs of the client BEFORE you enter the audition room, callbacks and bookings will be random or non-existent. Think about it seriously for a minute: how can you expect to give the clients what they need if you have no idea how to figure out what they need? Simply put: most actors don't know what they don't know about the audition process.