My advice would be to be certain you know what you're talking about when you read. Have the play read, get an annotated version from the library, mark up the script you get at the audition so that you know what you're saying, as Shakespeare's language is confusing, especially at cold readings. Make sure to ask if you're not sure what a certain line means. It's better than guessing, and there's so much in the audition that's already out of your control that adding that one bit of uncertainty can screw you up. In short, be familiar with the material. It's just like any other cold reading, as long as you understand the language and context of the dialogue. Good luck!
-Was that a fart?
-My fault, I fear.