The best thing you can do is make sure it's mechanically well maintained and that you keep up with fluid changes. The technical inspector is going to check to make sure your car is safe, with attention given to the proper installation of wheels, removal of loose items and properly functioning controls. You will want to confirm these things as well as check that the battery is tied down and secure. Drivers and passengers seat belts need to be in good working order. It is also highly recommended that you raise your tire pressures 5-10psi in each tire. In autocross there is a lot of load transfer, so increasing the pressures gives your tires more rigidity to manage the energy.