Lots of good advice here.
As CDH mentions, "eyes up" is an important and meaningful phrase you'll hear repeatedly through your training and beyond. Say yes to "eyes up" at every opportunity.
As George suggests, relax and enjoy the experience as you will likely be overwhelmed in your first baby steps learning a craft you currently have no skill set for. Be forgiving and kind to yourself when you find parts of the training difficult or challenging and be humble and help others if your the fastest learner in your group.
nyskinsfan has it absolutely right that all of the over thought prep goes right out the window when the training starts. You need to be in the moment with your ears open. It helps to have read Carl Lopez's "Going Faster" or the Bently books but you'll probably get more value from reading them after your training as you'll have actual seat of the pants references that will give the driving terms real meaning.
Tireman is the only driver who uses a recorder (that I'm aware of) and he's always the wiser for it. We are in an altered state having just stepped out of the car after driving and our ability to listen and process feedback can be limited. Recording your feedback takes the pressure off as you can listen back any time and confirm or revisit what was said. Notes are good too!
Arriving early and walking the track is a great idea both for processing the track and putting you in a relaxed receptive state of mind. If you can do it great. If you can't don't sweat it.
My advice would be to exercise regularly, eat smart and get plenty of sleep in the days leading up to your training. The days are long and you will likely feel tired each day. A nap isn't a bad idea but be careful, as some have taken a nap only to sleep through dinner hours leaving them unable to get dinner or fall back to sleep! (Doh!)
We all remember how excited we were and important it felt to be taking our 3-day training. At the end of the day it's your first step in learning a craft you'll hopefully have lots of time to learn and pursue. But even if it's the only time you ever sit in a race car, if you show up with open eyes, ears and heart you'll have three days you'll never forget at worst and three days that may change your life at best.
Good luck and have fun!