All you need for prep is a helmet!
Get out there and drive whatever car you have. Find out who the fast guys are at the events and ask to go for ride-alongs with them and watch what they do. Get them to drive your car during the fun-runs so you can see what the car is capable of. Ask them for tips on things like tire pressures.
If a choice in car is wide open, I would suggest a earlier Miata that you can pick up fairly cheaply. Great handling cars, plenty of people run them so you can get tips/info easily. Probably best handling bang/buck. I would suggest to stay in stock class if you can get a stock car, it's less hassle. Also, it's hard to make excuses about the car and how it's not prep'ed this-and-that, and that's why the guy in the Yugo is faster than you...
As you go up in prep level it gets harder to optimise/maximise the car and it also gets more expensive.
The main thing is to just get out there and drive. There is no subsitute to gaining experience.
Not to mention it's a hoot!