One suggestion. When you ride with a group that will obviously be faster than what you normally ride, just sit in. There is no need to pull through only to blowup shortly after. Just let the faster riders know that's what you're doing so there is no confusion.
There are two ways to do that. One is to stay at the rear and the other is to rotate through but just pull off when you get to the front. I would prefer the rider to rotate through if he/she was comfortable with the paceline.