Get set to have some fun.. Long..
All the advice you've received about getting with a group is good. Some thoughts on what you may find on rides with most groups, and a little advice on how to fit yourself into the pack. The 'dynamics' of riding closely with others is a fascinating study . It's what makes road cycling unique.
Groups of riders who're very familiar with each other will develop their own style, but basic pack riding ettiquite is the same for every group. If you know an experienced road cyclist, ask for a short 'lesson' in what's expected of each rider when riding in a group. That way, you'll be a safer rider on your first group ride. If you don't know any experienced road riders, ask someone at the back of your first group to help you out with hints. Most packs will have a "mother hen" type who just loves taking care of new riders or strangers.
Remember, when using the draft, the riders behind can't really see ahead, so each is responsible to point out potential hazards in good time for the following rider to avoid. If you'll shortly be sitting up, or there's is a loose doggie ahead, or or or..it's your job to let the following riders know. Please learn this. It's a good idea to spend some time at the very back of the pack and watch how this works. Pointing out hazards becomes second nature very quickly for most riders. Trailing along at the back is also a good way to spot the flakey riders in a group. When I ride with a strange pack, I usually start a few bike lengths off the back and check out the skill levels before I totally commit myself. If I see a potential problem rider, I keep him/her in mind during the ride. Conversly, it gives the others a chance to asses your bike handling skills and fittnesss level before things "get serious"
The nature, the tone of a group ride can be vastly different, as has been stated. You just have to see how each group is going to be. I usually ask a new group to "leave me, if I am too slow" That seems to releases the group from feeling bad about maybe dropping a strange rider who's skills or fitness might not be up to the ride. On the other end of the spectrum, we've had strangers who've joined our club/team training rides and decide to "Put the hurt" on the whole group. That never works, at least with our group. When a "new guy" comes out to ride, without seeming to, the whole pack is assesing him/her. A little humility never hurts. The "pack" is like an entity..a competative entity. It hates to 'eat crow'! A large number of riders are stronger than a single rider..duh!..so if a newbie challenges our group, he gets quickly hauled back into the fold...unless he is a total jerk..then he's left out front, alone, until we, the pack, decide to slam-dunk him.
Group rides are soap operas, too. Or perhaps like a 'survivor' show. There are predictable roles in most packs. The ALPHA rider, the hill guy, the explainer, the whipping boy, etc etc. That is what makes it really fun.
A few things I'd like to see less of while rideing in a pack:
The rider who rides alongside, talking talking talking, and when the call from behind "Car Back!", comes, they just *have to* finish the paragraph, make their point, before dropping back or moving ahead to let the vehicle traffic pass. That's rude and makes us cyclists untold enemies among the vehicular crowd. Stupid to make enemies. Whatever some Saturday cyclist is saying to his 'victim" (the "listening" rider is usually pinned, by the Rapper, against the shoulder of the road, with other riders in front and in back) can certainly be delayed until that ******* in the dump truck (or whatever) is allowed to continue past on his own important journey. Remember, motorists usually think cyclists are 'weird' and we 'have too much time' and we're ******* and we're blocking thier road..etc etc. And Polar Bears think humans are food...I'd rather not piss either kind of oversize predator off needlessly.
And don't ride with an overlapping wheel when drafting. Pay attention and stay behind, all the way behind, the person you are drafting in a paceline. If it's a side wind, still stay back. I'd guess most big crashes are caused by a rider with an overlap getting his front wheel clipped, going down and everybody behind has a big problem! Even for just a second, if you stick your front tire past the guy in front, and he swerves just then, without warning to miss a hazzard, you are going down! And so may many following riders.
Mostly, have fun at this newfound sport..
Don Hanson