There are groups and then there are groups. My cycling club's rides are "group" rides, but that doesn't mean that you will necessarily be riding in a paceline or drafting. You can if you want, but you can also just do your own thing. In contrast, you can pretty much expect to be in a paceline at our club's weekly training rides. So, you might get more specific advice if you can tell us more about the group you're planning to join. Is it an informal group of riding buddies, a club ride, a training ride, a group geared for new riders?
As a general rule, however, I think you need to know how and when to use both hand and voice signals to announce traffic, road hazards, turns, changes in the pace, traffic signals and the like. You should feel comfortable not only dodging road hazards but alerting others to their existence, too. You mentioned that you aren't great (although the contacts may help) at dodging potholes. I would suggest that you get better at this before you ride in a group or let anyone draft too closely behind you.
To ride in a group, you should ideally be able to ride in a steady line and should aim to ride predictably. You should be able to look over your shoulder and take a drink from your water bottle without weaving.
If you're riding in a paceline, you should be able to ride at a steady pace, have a steady "spin" or cadence, and not brake excessively (at least without annoucing that you're doing so). My biggest pet peeve is riding behind somebody in a paceline who coasts every few pedal strokes. That sends mixed signals to the person behind you that you're slowing down. But given the experience you've indicated, I would avoid riding in pacelines just yet. Get comfortable first just riding with people in a loose group.
Before joining any group, I think you should have some idea of the ride and the group's expectations of you. Is the route marked and/or is there a map? What's the expected pace? Does the group have a no-drop policy? Do they have meet up points if people get seperated? How long is the ride and are there any stops along the way if you run short of food or water?
My attitude is that it pays to ask questions and to be honest about your experience and abilities. Usually, someone will be happy to show you the ropes if you make it known that you're new.
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