First of all, take it easy on yourself. It's not that bad and most will probably help you out.

Dress nicely, but don't overdress. Shirt and cotton/khaki pants with dress shoes should cover unless they require a tie.

Take lunch with you just in case; if they go out, go with them.

Introduce yourself to your group, if your supervisor hasn't done it already. I used to smile a lot when I was new, that's with most of us out here I guess. Smile, but not nervously.

You're going there to work, focus on that. Not what others will do or say.

Good luck for a long and fruitful career.