I would first try to talk to the group ride leader and explain the position your in. Etiquette: If this is your first group ride try not to spit or blow your nose on anyone, which means, if your in the back, do what you want, but anywhere else and be aware. I hate it when people spit and I get their junk on me .
As for safety, just be sure to be steady when you ride. It makes people nervous and you nervous if your steering is real jerky. Try to find a wheel that is steady to follow. That will help you stay steady as well. Let people know when there is crap on the ground like glass or a hole and signal where (or yell) and let people know whether or not your slowing. It's funny and scary when I ride with the fast group b/c they never say anything and the potential for crashes is truly frightening but when I ride with my ladies group, no problems, people know what's coming their way.
If anything, find someone to take you under their wing and show you the ropes. When I first started group riding, my group had a beginners training session and beginners group (for those who couldn't make the sessions). Or, if there is a group of you who haven't ever ridden in a group ride, maybe ya'll could start a beginner's ride with a few experienced riders to help you along.
Hope this helps and of course, have a great ride!