Riding with a potentially large number of people takes a little more awareness of yourself and what and who is around you. Generally speaking, I'd encourage you to stay to the right of the road unless you're passing. If riders are close behind you, it's nice to yell or point out any road hazards and to signal when you're slowing, stopping, or turning. As you pass other riders, yell "on your left." Always keep an eye out for what's behind you, especially as you go to pass someone. If I had a dollar for every fast-moving cyclist or paceline that passed me on the left without warning, I'd be a rich woman. If a car is coming up from behind, yell "car back." From the front, yell "car up." If a car is passing, yell "car passing." This assumes othe riders are nearby.
One pet peeve I have at event or club rides is the yo-yoer. Those are people who pass you and then almost immediately slow down such that you then have to pass them. Then they pass you again. Don't be that person!!!
Otherwise just have fun! Be careful at rest stops. It is easy to overeat at stops. And don't stay too long at the stops--unless you don't mind having legs that feel like lead!
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher