Take powder to clear Fire Ants. Those things really hurt when they bite.
Don't bother with a long lens for your camera - catch fencing is minimal at Sebring and you're almost on the track.
Make sure that at the very least you visit Turn 10 - there'll be a Club Arnage Flag or Banner there somewhere - great viewing at T.10, and marvellous company who will always chat.
Get involved in the Party - The Party Barge, F-Troop and "Hank and Sheilas Frikking Big Tent" are all must sees.
If someone offers you something to drink from a Jam Jar, don't drink it like Lemonade. (Lesson learnt).
If someone offers you "cherries" - don't eat 9 of them in 10 minutes unless you're sure. (Lesson learnt).
If someone offers you "Pineapple" - eat it. It's lovely. But make sure you're sure.
Sebring 2012 was one of the best events I've ever attended - the people, the track, the noise, the people, the party, the people, the booze, the party, but mainly the people. You will have an absolute blast. Be aware that it IS slightly different to Le-Mans - less tolerant of complete Bell-ends from what I can see - but that's what happens when you replace the weedy Gendamerie, with American Cops. With Guns.
Have a great time!