If you don't often ride in groups, please remember these points:
1 - Slower riders stay to the right, pass on the left. Avoid passing on the right.
2 - Do not overlap wheels. If you are riding close to another rider, do not remain in a position where the other rider's rear wheel could hit your front wheel if he slowed veered towards you not realizing you were there.
3 - Maintain your situational awareness, don't zone out.
4 - Ride in a straight line ("hold your line"), anticipate when you need to reposition to avoid potholes and other riders so you don't need to make sudden changes.
5 - At rest stops, make sure you signal your intentions to stop and look both ways when re-entering the roadway. Look out for gravel. Don't stand in the roadway. Not everybody stops at the rest stops.