Godly luck, sir. I still wake up in a cold sweat every now and then remembering my CFI initial.

Know the systems in and out of your aircraft. Recite private,commercial and CFI endorsements. For heavens sake, know airspaces! Be able to teach 8s on and lazy 8s - since those are a more difficult topic and draw on almost all topics, examiners at my school LOVE to test those.

Most importantly - take breaks! I know there is a urge to "finish things up" but seriously, give yourself a breather. My CFI oral was getting rocky and I was on a slippery slope downhill and I just said "look, I need a few minutes to collect myself and get back into things." Had to do that a few times but managed through it.

Also, bring a bottle of water. You're going to be nervous as it is and since you will be talking the whole time, you're mouth will get dry.

Again, good luck!