Just make sure that the car is in fit condition really...
First check that you do not have any oil or coolant leaks and that rad hoses are not likely to split.
- make sure you have some decent meat on your pads.
- check oil, coolant & brake fluid levels are as they should be.
- make sure that your tyres have enough tread for you to do the day and get home again (legally!)
- Make sure wheel bolts are at the correct torque as over tightening can in extreme cases cause warping of the discs.
- Re-check the above when you come in after a session as they can slacken with the heating up and cooling down.
- When you park up in the pits, dont leave the handbrake on and the car out of gear - instead leave it in gear with the handbrake off. If you are on a slope and you do not do the above, you may end up chasing after a run away car...
- Set a max limit for number of laps depending on length of track possibly. I usually go out for 10 laps or so and then allow the car (brakes, oil, coolant etc) to cool down before going out again.
- If you feel the pedal going soft - do not keep hammering it for one last lap - take it as a warning as you will probably lose all braking as you have boilled your fluid.
- You do not need any 'special' modifications as such, if you do any, fit braided hoses along with a proper brake fluid like Motul RBF600 as your brakes will last far longer.
Also, something I have learned, if something does not feel right with the car you are usually right! Just take it in and give it a quick check for peace of mind. I chose to ignore a funny vibration and a wheel later came off!
Other than that, just take it easy, have fun and remember - it's not a race!