If it's your first track day, I'd just suggest getting (even borrowing) a helmet. Make sure *everything* is out of the car - your phone, coffee cup, stuff in the trunk, ice scraper, floor mats, etc.
Make sure your tires are properly inflated, make sure you have at least 1/2 of your front brake pad thickness left, make sure your fluids are at the right levels, and make sure your battery is bolted down.
Then go have fun!
Any respectable organization will pair you with an instructor for a day who will work with you from the right-seat to explain the driving line, smoothness of inputs, what to focus your vision on, and so much more!
Eventually there are a ton of mods you can do, but, remember, the longest journey starts with the first step! Just get out there and start doing it - you'll have plenty of time to figure the rest out as you go along.