There are several sources on the web for tips on how to safely ride in a group. All of them serve up helpful advice which looks great when you're sitting in front of your computer but somehow gets lost when you hit the road.
Two simple key riles will help you keep yourself out of trouble when riding with a group:
1. Keep your eyes wide open. Be aware of what everyone else in the group is doing. Be as self-aware as possible, keeping an eye for changes in the road ahead, the traffic and your fellow riders.
2. Communicate with your fellow riders. Talk about what you're trying to do as a group. Communicate changes in the road, any traffic or other obstacles
That is a quick synopsis. However, the following video gives much more detail. I strongly suggest you watch this one often.
https://www.youtube.com/watch?v=O8vJsRrhM1c
