For you:
Take water (to drink!), and sunblock. Wear good shoes you can stand up in for a couple of hours when you work course. Take lunch, or a snack at least.
Walk the course.
Talk to people who have done it before, they are a wellspring of information, especially if anyone else is, or has run a Fiero. They were/are very popular for autocross.
Walk the course with said experienced person, then walk it again alone.
For the car:
Something you may not expect: If you care about your paint job, wash, and wax a day or so before you go. The wax will provide a nice layer of protection that lets you take cone marks off easily. (big black marks typically, like old rubber shoesoles on linoleum) The wax is the important part. Doesn't have to be any special kind, just something. The wash just keeps you from waxing in dirt

I would add air to the tires, typical street tires have a tendency to roll under at the more typical 32-35ish psi. If it's bad enough, you can roll the tire off the rim, then you're stuck running a donut, or walking home! (if you have separate track tires on their own rims and you take both sets along, obviously there's no problem there...)
Take chalk or something you can mark the tires with, and mark the sidewall right up next to the tread and go a little onto the tread. If you are rubbing off the mark on the sidewall, you should add some more air. You want the wear to be right up to the edge of the tread. (A tire pyrometer is also good for this, but expensive)
Me, I run at 50 PSI cold. You can probably get by with 40-45 or so, depends on how stiff the sidewalls are on your tires.
1st run: HIT CONES! If you're not hitting any cones, you're not pushing any limits, which likely means you can get closer.
2nd run: Don't worry about hitting cones, but try to keep close.
3rd run: Try to clean it up, but stay tight. You should be getting the feel for it by now.
4th run: Have fun!
(some regions get 5, mine gets 6 total for the day, but the idea is the same)
Last run: BONZAI! <-- that's what I do anyway, especially if I have a decent time on one of my other attempts.