Hand-Signals: It is not imperative that all the cyclists in the group point out the same hazards or signals, as long as a few are. If you are a beginner or unsteady, then is far safer for the group for you to keep both hands on the handle-bars than it is for you to point things out.
‘Slowing or stopping’
‘Obstacle’ or ‘car’
‘glass’, ‘pothole’, ‘bollard’, etc to identify a hazard