know airspace, and your sectional charts. even if you look at a Class-C airspace on the sectional there are 10 things that you can talk about it. I made sure that my FAR/AIM book was tagged with subjects. If your examiner notices that you are organized with flight planning and paperwork that will surely impress him. Also take your time while you answer the questions, dont rush into it. Take it easy you wont be signed off unless your intructor thought you were ready.
O BTW teh ASA oral prep book helped me a lot. i was confident and passed the oral exam with flying colors.
Remember take your time while you answer your questions and dont BS your examiner. If you dont know jsut tell him "i dont know, but i can look it up and we both can learn something". As an examiner knowing everything he wont be cocky with you, infact he will appreciate your people skills and help you out. All this is coming from personal experience.

again Relax