When road riding with a group, following cycling etiquette ensures a fun and safe experience for all: Relax and maintain a steady, predictable line (wobbly riding can cause a crash). Remember that people behind you may not be able to see what you see in the road. Alert ride partners to hazards such as potholes and debris by shouting a warning ("Hole!") and by pointing it out so they know where it is. Brake sparingly because riders behind have to brake harder than you did, since they are reacting to you, which can become a dangerous chain reaction. When standing to climb, your center of gravity shifts, which might cause you to thrust the bike backwards. This can scare ride partners and even cause a crash. To counter this tendency, as you rise out of the seat, continue to apply power to the pedals so you don't slow or move backwards.
Probably the most important rule of group riding is good communication. Ideally, the leader will explain the ride in advance pointing out any safety considerations such as rough roads, high-traffic areas, easily missed turns, etc.
If no one seems in charge, you should speak up and ask, because sometimes there is no formal leader and the assumption is made that everyone knows what's going on simply because they've come out for the ride. This is sure to cause problems. If you don't know, ask, and keep asking until you find someone who can tell you what's going on. There are always a few people who know and are willing to help and it can make a big difference in how much you enjoy the ride and how safe it is.
Once the ride is underway, you can learn a lot about a group by watching the other riders. Try to find and avoid those who wobble and speed up and slow down. These are signs of poor handling skills and possible fatigue that can cause a wreck. Instead, try to ride with the people who hold a steady pace and a straight line because they're less likely to do unpredictable things that can cause mishaps.
Don't Overlap Wheels
When cycling in a group, always pay attention to where your front wheel is in relation to the person in front's rear wheel. Keep your front wheel behind his rear wheel, not overlapping it. Why? Because, if he suddenly veers to avoid a hole or rock, his rear wheel will knock your front, which will send you flying.
Use Care When Looking Back
Another extremely dangerous maneuver is turning around to look back like you might do if a friend was on the ride and you were trying to figure out where she was. There's only one safe way to look back and it requires a willing helper. To do it, ask the person next to you if you can rest your hand on their shoulder while you look back. They'll say yes and you can then hold on and look back. Having your hand on a shoulder prevents you from swerving as you look back and it keeps your bike going at the same speed as the other bikes preventing slowing that could cause problems. Practice this tactic with a single riding partner before trying it in a group.
Finally, there's the challenge of expectorating in the peloton (a bike racing term for what the group is called). Everyone has to do it, so don't hold off. But, do it carefully so you don't soak your ride partners and get banned from the next ride. Always spit with the wind and away from riders. If this means steering to one side of the road first, go for it (but only when you're sure it's safe to move over).