Recently, I have had the opportunity to begin to go on group rides a little more, although my pace is unfortunately slow at the moment. I feel like I am finally when in a group getting the hang of drafting and riding with people, where previously I rode a lot on my own and people made me nervous. When you ride alone, you don’t have to worry about drafting or someone behind you, but in a group there are a lot of other potential issues.

Know your pace. Right now, I am with our C group, which is 14 mph and up, but when I am in better shape, I am a B group rider, which averages 17 mph normally. Typically you will be faster in a group than on your own, but pick the group that is your speed and stick with it. Normally you will all progress similarly, so you still have a good group to ride with. If you are on a group ride that is a little faster than your usual pace, but you can hang on, sit on the back and let other riders know you are staying on the back.
No aero bars. You can ride your Tri bike with some groups, but no getting in aero bars when in a group on a road or Tri bike. This is for the safety of you and the other riders. I don’t care how good your bike handling is. If have to brake for a sudden red light and you’re behind me in your aero bars, there is a good chance of us both crashing.
Know your pace lines. Most groups employ either a single or a double pace line and will have their set ways of pulling off to the back. In a single pace line, the rider in front will typically signal they are moving to the left and going to fall to the back. In a double pace line the riders will sometimes split to the left and right, or they will both move left, so I suggest starting in back or asking if you are unsure of how the group tends to ride. My biggest pet peeve is in a double pace line when the person next to me will ride between two people instead of on their wheel.
Know your signals. The two most basic are your turn signals for left and right. Beyond that, we also want to point to either side and announce things like glass, potholes, and gravel. I also suggest knowing signals for slowing/stopping, and announcing this as well.
Announce cars. If you hear a car and you are in the back, call out that there is a car back, so everyone is aware and if you need to move to a double pace line you can.
Maintain a steady pace when pulling. This can be a fast pace, slow pace, or a moderate pace depending on the ride, but the goal is to maintain the pace the ride is intended to be. If you are about to pull, look on your computer to see your current pace and try to maintain that when on the front to avoid going too hard, which is easy to do.