Smoke a joint! hahahahaha ... joking. Dude ... just mentally prepare yourself. Think that it is gonna be nothing and know your shit good. Think that it is there loss if they dont get you.
Most importantly ... ASK THEM questions. Make it a 2 way interview. When you ask them questions, regarding the job and the questions that they are asking you, it will put them on the spot a little and turn the tables a bit. It seems like a 2 way communication then, and less of a grilling towards you.
Good luck ... whatcha applying for?
Mavy