I second the leisurely pace/warm up.
One of the reasons I don't like group rides is the tendency to go out the door at 18 mph. I just can't do that. I couldn't do it ten years ago and now it's even more important. On almost every group ride I've done, I am just starting to feel good when others are fading. One guy who used to lead rides we did was notorious; I asked, as a fellow leader, to please have a warm up, as we often started going up a hill. He never did change his ways.
2015 Trek Silque SSL
Specialized Oura
2011 Guru Praemio
Specialized Oura
2017 Specialized Ariel Sport