Look...Listen...Learn. Speak when spoken to. And if you can, write down your questions for the first day or so (as opposed to asking them as they occur to you). Odds are many of your early questions will be answered naturally as the first few days go by. Anything that is still unclear by mid-week should be asked in an e-mail (if that is an option) or at a scheduled sit-down with your boss/trainer. Bring money for lunch on the first day, even though you should plan on bringing your lunch regularly after that. Hopefully some people will be going out/ordering in lunch and you will want to participate if the opportunity presents itself. Also, if things are getting stressful it's nice to be able to go out for lunch and step away for a little bit. Dress nice (no wrinkles). Smile. Focus on the fun/excitement rather than the stress/uncertainty. It takes all of us a while to feel like we belong and to get comfortable. Be nice.
Good luck.