Be prepared. Already be rehearsed and memorized. For the sake of everything awesome, don't try and wing it. Many people are getting paid to wait on you when you're trying to learn your lines in the moment. Everyone has slip-ups, but your main homework should be done before you even make it to set. Knowing your script is your main job as an actor.
Leave your problems at the door. Your focus shouldn't be how parking sucks or how you wish there were Green tea packets instead of Earl Grey. When you arrive, you should be clear-headed and available to take on everything the job will throw at you (And, trust me, it'll always throw down) without bringing your personal problems into the mix. Everyone is there to create something great, so make sure you're also ready to kick ass and create. (P.S. I repeat "You're Meryl Streep" to myself at least 3 times and make sure I take my vitamins. I suspect it's the reason I'm mildly successful)
Learn how to take direction. When you do a take, and the director asks for something a little different, there's no need to go into a diatribe as to why you made the choices you did. You're an actor; you should love getting redirected. You don't need to justify yourself; you've already got the job! The director is there to tweak your performance because that is their job. Getting directed is one of the most fun things about being an actor because you get a chance to do it all again in a totally different way!
Don't be an asshole. Being on set is like being part of a huge family for the day, and if you're rude to one of your family members, it's not a good look. Just because the PA isn't the one who hired you doesn't mean you shouldn't treat them just as kindly as the director or producer who did.
Love the process! Yes, you'll get moved around and probably have to wait for hours in some cold room before you even get a chance to do your thing, but that's just part of the process. Consider yourself lucky to be waiting on something many people want to do but never get the chance.
Listen. Listen. Listen. 15 things are going on at every moment when you're on set, but you need to be on your toes. When the Assistant Director tells you what's coming up while you're getting your mic on and wardrobe is powdering your nose, you'll be thankful you listened up in the midst of the chaos. It'll not only make you look good when you hit your mark and deliver cues, but it will also keep the production on time. You don't want to be the actor who couldn't deliver and then turned everyone's 8 hour day into a 10 hour one. Time is money, and productions are always looking for ways to save some of that green stuff. Be the actor who made the producer stop cursing about the budget and the ticking clock.
Have fun! You made it this far. Being on set is just the icing on the cake. Don't let those nerves tell you any different. You've already delivered in your auditions, so go out there and do your thing. Trust in your talent, and everything will fall into place exactly as it should. Then take yourself out for a cocktail when you wrap because you're living the dream, baby!