Make sure your suspension is in good order.
Check your brake lines, pads and discs for wear perhaps think about upgrading your pads if they are stock items.
Check your tyres have plenty of tread and the pressures are good
Check for oil and fluid leaks,
If you are planning to service the car do so just before you go, new oil, brake fluid will help a lot.
Take some basic tools, cable ties, gaffa tape, workshop towel etc.
When on track make sure you always have more than qtr of a tank so you don't get fuel surge (unless you already have a swirl pot)
Dont go mad straight away do a few laps at 60-70% of your limit this will allow you to adjust to driving on track.