Have a full tank before arriving at the departure point.
Tell the group leader if you have any special concerns, i.e. speed, sharp corners, etc.
Tell the group leader if you plan to leave the group before the destination. Also tell the persons riding in front and behind you so they don't think you are having a problem.
When a rider leaves the group while in staggered formation, the best way to compensate for the hole made by his absence is for each rider slide up and NOT over.
Tell the group leader if your bike has an unusually short fuel range or if your bladder has a short range.
It is not unusual to start out on a ride when it is fairly warm and have the temp cool down a lot before getting home. Riders often wear a light jacket because it felt fine at the time of departure and really be freezing after it got dark.
Remember to take some clear eye protection if the ride will extend into the evening.
When exiting a expressway, keep up the pace so the riders behind you aren't forced to slow down while still on the expressway and become a traffic hazard