Take it a little easy on your first run just to get the course down from the perspective of the car. Walking the course is just to get the layout of the course so you won't be surprised by anything. Driving the course is a whole other experience. Gradually increase your speed through the course on each run. It's a good I dea to get an experience person to ride with you on at least the first run to make sure you are going the right way on course(this will help you avoid the dreaded DNF) and to give you pointers about what you did wrong and what you did right.
-Slow in, fast out. Brake in a straight line before the turn and accelerate through them.
-No jerky motions on anything. Not on the steering wheel, brakes or gas. Try to do everything with a smooth input and motion. I don't mean slow, I mean smooth, there's a difference. This will take a while to get right.
-Look where you want to go to, not where you are at. Try to point your chin up so that you keep tour head up and are looking ahead to what's coming up next. Look for the exit of a turn, not the apex or the entrance, especially once you are entering the turn. DON'T aim for a cone, you will hit it! Don't look at your speedo, or tach or steering wheel. You will go where you are looking, just remember that.
-Get into second gear and leave it there. Do not switch gears no matter how much you want to(with the exception of starting in first).
-Remember to unwind your steering wheel as you exit the turn more than you think you should. You can do this more than you think in the MP3 and it will keep you from pushing(understeer) and scrubbing off speed. This will take a while to learn as you have to try it to the extreme a few to time before you really trust that the car can pull you through it. This is something I learned recently and I'm still getting used to it three races later, it's somehting that you can't pull off in any other car.
-The inflation rates in the other post are the way to go with the stock street tires. You can control oversteer(how loose your rear end is) by increasing and lowering the pressure in your rear tires. More pressure=more oversteer, less pressure = less oversteer. 38psi should be a nice compromise.
-Buy a good tire pressure guage($10-15 is a pretty good guage). One that has a pressure release valvle that makes it easy to remove pressure from the tires. Inflate your tires at the gas station before you go to higher than you need then bleed them down when you get there. Don't worry too much about messing with the pressures after every run, pay more attention to your driving and what's going on as far as the grid moving and such. The only thing to worry about is if the rear end is sliding around too much then bleed off a couple pounds in the rear.
-Bring something to sit on, something to drink(water is best), something to eat, and sunscreen or a jacket depending on the weather.
-If you have a torque wrench, torque your lug nuts down to at least 70ft./lbs. If you don't have a torque wrench, see if you can borrow one or buy one because even if you never race again it's a good thing to have in your toolbox. Our stock lugs are 21mm(which seems odd to me, I changed mine to a 3/4" size.) Basically, just make sure the lugs are tight even if you don't use the torque wrench to check them.
-Oh yeah, have fun!
Some of the stuff I'm telling you above is a little more advanced stuff than what you should focus on in your first auto-x but keep it in the back of your mind to think about after your runs to analyze how you can be better.