Go over the character breakdown and plot synopsis, if available. The breakdown and synopsis will guide how you frame your character's dialogue delivery and stage actions.
Watch previous episodes of the television series, if available; doing so will allow you to grasp the nuances of the screenwriter's dialogue, as well as the traits of the director.
Mark up your script with the notes you have made on the delivery of the dialogue and the blocking of the scene. Add notes for any words that need emphasis, and for any pacing changes and vocal inflections you wish to add, creating a true character.
Go over your script and act it out in front of a mirror. Bring in a fellow actor or an acting coach to give you tips. Make yourself aware of any mannerisms that you develop as you practice your lines and blocking. Create a true character using these mannerisms.
Remember to stand where told when you enter the audition facility. When you are told to slate, look directly at the camera and give the information the director or casting assistant asks for. If they do not ask for specifics, say your name, the character you are auditioning for and your phone number.