Rent some kind of fan scanner. They have different kinds you can get. I would get Nextel FanView, to me that is the best one.
Since it is your first time, you will need ear plugs, cause if you don't, the loud sounds are gonna hurt your ears alot. Those engines are louder than it looks.
I would bring a back up pair of shoes.
Be ready for the weather. In Atlanta, one day it can be 65 degrees and the next day its in the 30's. So make sure you bring proper clothing.
You are going to need sunscreen just in case it's a sunny day. Sitting in the sun for 3-4 hours is a good way to get a sunburn.
The concession lines are usually packed, especially around pre-race time. But as H8Gordon said, I would do it at off times so you don't have to wait in a long line, risking the chance to miss the start of the race.
The souveniers are a good way to stay updated.
You can't avoid the traffic, if you leave for the track early or late, the traffic will be bad. So I would leave early to get you some extra time in case the traffic is really bad.
If you are wanting autographs, some of the drivers will sign them if you ask them. But ask them politely.
The main thing is to prepare properly. Bring coats, proper clothes, sunscreen, etc and you should be good.

Make sure you reserve a spot for Monday incase the race gets rained out. Nothin like paying money and not seeing a race.