The more you ride with this group, the better you will get to know some of the other riders' habits. See who handles the bike well, and try to get behind them on the rides, or just say you are more comfortable in the back. (Someone has to be last, so why do they care if it's you? Or is there a sweep?)
I have trouble letting go of my bars to signal for everything, so i do a lot of calling out.
Good luck! I've learned so much from my group rides, hope it improves for you.