Get good rest the night before, don't drink alcohol that night. Drink a gallon of water a day before and a gallon each day of training plus at least some gatorade or electrolyte stuff.
Don't talk about what you think you know or who else you've trained with. Your paying for THIS instructor's take on the subject, try to apply it, even if at first seems odd to you.
You mentioned an entry level course- don't touch your weapon at all when your not supposed to. It's not the time to finger fudge your gun, show it off to others there, etc.
Too often people show up to their first class all amped up just like a kindergarten at their first day of school- "all these kids, sooo much fun, yippeee!" Relax, breathe. Your learn more and be safer calm and moving slow. Don't be that guy. If you don't know, go slow. Too often people get the "I don't know what I'm doing but I'll try to do it FAST" approach, which can be borderline reckless. If I haven't trained with the others before, I try to get the far right hand spot on the line....