castle offered great advice, above... a few more thoughts...
Be sure you know the tech requirements for the track day organization you're running. And get those issues settled
before you arrive. Try to take care of as much of the details beforehand (bike prep, tires, etc.), so that you have nothing over which to stress about once you arrive. Arrive early, with plenty of rest. Take lots of water and keep hydrated.
For the first time out, breathe, relax, and focus on
smooth. Pay close attention to the rules for the organization running your track day... ask questions if you're not sure. Know the flags and watch for them at corner stations and at start/finish.
If you must come off pace, get your hand up and do so abruptly. Do not delay. It's a great habit to form from day #1. So many times I see folks that see a flag or a crash or whatever, and they'll just chop throttle and sit up... do not do this. If someone is riding agressive and close to your 6, you will find yourself in serious peril. Get your hand up first, and smootly come off pace and off the race line.
If it's a red-flag (ends the session), don't slow down to 30mph. Get your hand up, come off race pace, but keep a good pace so you can clear the track quickly. At most track days, the EMS cannot attend to the rider down until bikes clear the track. So be safe, but be expedient.
If you signal that you are going to pit in (raising a hand or extending a leg), then get off the race line and pit in. Do not change your mind and come back on to the race line for another lap. If you do change your mind and want to go for another lap or two, fine... pit in and the track marshal will clear you to go right back out when it's clear.
Do not stop on the racetrack. Ever. If your best friend lowsides in front of you, do not stop. If your mother lowsides in front of you, do not stop. If you experience mechanical failure, get your bike well off the track to a safe location and look to a corner marshal/worker for direction.
If you do see a rider go down, do not look at them. It's called target fixation, and it's trouble. It's very difficult not to look at them, and nearly impossible not to run over them if you do. Force yourself (rehearse this in your mind) to look away and focus instead on your intended line.
As castle stated, ask lots of questions. If you need help, ask. If you see someone else needing a hand, offer it.
Have fun out there!
