One thing that wasn't mentioned yet. On your "first" track day you will be in a novice class. This means you will typically start your day in a classroom. You will follow a coach the first couple sessions at a slow pace to learn track, lines, ref markers, etc.. You will be starting out slow no matter what. Then once they release you slowly up your pace! Best tip I can give is don't enter corners directly behind other riders. The slower riders will brake VERY early and could be a disaster. Give yourself an open lane on corner entry!
Also, once they release you don't go WFO. The speed you will be used to behind a coach is alot slower then what you will be used to if you hammer down your first opportunity. Track days pay nothing! So like others have said, take your time building pace, look as far ahead as possible, and of course have fun!
You will not be the fastest guy there! No one cares how fast or slow you are so take the time learning the track and getting technique consistent.
After this, next issue is a 2nd job to pay for tires, track time, parts, tires, and track time!