Riding in large groups?

Howdy, welcome to the roads. Be smart and careful. It's fun and way dangerous. Besides having a great time, my primary need upon finishing a ride is to remain unhurt. So, as biker & driver my golden rule is: "stay, or, get out of the way".
Cars, they're heavy. Drivers - don't make them angry. Look directly into the eyes of a driver, make eye contact.
Ride in the direction of the traffic flow, and always ride single file in traffic. When in a large group, get away from the group (I say). In particular stay away from morons riding 2 and 3 abreast on well travelled roads. They're assisting in the creation a bad situation, firstly for themselves, and secondly, for that single rider, 10 minutes later (maybe you or me) whose being overtaken by some driver who was stuck behind 3 bikers who refused to single file and let him by. (true).
Heh, have a little respect and be careful. It's a blast. :o

Keep your head up, stay off the brakes, hold your line, and don't overlap wheels with the person in front of you. It helps to get in some rides with smaller groups before diving into a big pack.

to add to the others:
listen to the riders in front and behind as they are constantly warning about traffic ahead and behind. Feel free to shout out if you hear a car coming from either direction ( I usually ride in rural Illinois)

Also watch for hand signals warning of debris/potholes. gravel in your path. The rider ahead of you will move their hand from side to side in the direction of the upcoming situation...... Likewise if there are riders behind you, you need to pass the warning on. Let the riders know you are knew and they will be pleased to teach you as you go along. Riding in a group that is single file and blasting along the road is one of the great experiences, enjoy relax... pay attention to your surroundings.

I'll probably get some vehement disagreement about this, but I'd advise NOT riding in pace lines. It's just too dangerous, and raises the already high risk of cycling on roads even higher. Whenever I've espoused this view, I have people say, "Well, only ride in pace lines with experienced riders." But the pros bring each other down all the time! In just my hometown I know of so many local riders who have been badly injured in pace lines, and it continues year after year. Now multiply that by all the other hometowns in the country (and world) and I think it's a tragic and avoidable situation.

My opinion is this: Unless you have professional or serious amateur road-racing ambitions, pace lines are not worth the risk. You can still get very fast and fit, and race in time trials. Leave the broken bones, concussions, and spinal injuries to those who are getting paid for it, or to those who are still young enough to think that that sort of thing couldn't happen to them.