Now if you are reading this because you got your first job, then allow me to congratulate you. Good work in passing the job application and interview process. You had gotten far now. You fought the job-snatching-gladiator battle and came out victor. I think you should take a deep breath and relax. Treat yourself with someone nice, could be a peaceful night reading a book, buying yourself a nice mousse cake, treat your friends/family to dinner... just enjoy yourself. You deserve it.
Be on time! By god, I was there 40 min early. I waited outside on a picnic table for 10 mins before I gathered enough courage to walk in. Apparently, my boss saw me from the window and LOL-ed. Gosh, that was embarrassing!