Don't be a lemming if the group engages in unwise riding behaviors.
Ride NO CLOSER than a two-second delay (one-thousand-one, one-thousand-two) behind the bike directly in front of you, or a one-second delay behind the bike diagonally in front of you. Groups accustomed to riding together often get sloppy about this, but tailgating can lead to deadly bike pileups. Err on the side of riding a little "loose" to give those in front of you plenty of room to maneuver in an emergency. Always loosen up on corners to allow riders in front of you to choose the best cornering line for their bike, which often means using the full width of the lane.
Look for bad road surface, crumbling shoulder, narrow lanes, etc, and signal for single file if the travel lane appears unsafe or uncomfortable. Traditionally this has been a judgment call left to Road Captains, but in our club each individual rider shall have the authority to make that call.
Road Captains practice slow take-offs, hand signals, working with a Tail Gunner to change lanes smoothly, no abrupt moves, and always "riding for the group". Tail Gunners keeping other vehicles from tailgating the group, warning the riders ahead when a vehicle appears to be drifting into their lane, helping with lane changes by securing the desired lane upon the Road Captain's signal, etc. Various members will end up in those positions when large formations are broken into smaller groups.
Bikes traveling in formation are most safely grouped in fours or sixes, preferably with a visible gap--an extra second or two--between each smaller group. This enables safer movement through traffic by providing natural breaking points where cars can merge, and also makes lane changes more manageable since they can be done incrementally.
If the formation gets interrupted by traffic, red lights, etc., the group in front should slow down if possible, but not pull over unless it's an emergency. The group in front should continue at 5 or 10 mph UNDER the speed limit, while the group(s) in back continue 5 or 10 mph OVER the speed limit. This will usually result in a gradual, orderly rejoining of the whole formation. Once the formation is complete, the road captain can accelerate to normal speed and continue on. If the front group reaches a major turn-off before the back group(s) rejoin, he/she can signal and pull over in a safe place to make sure the back group(s) don't miss the turn.
In a twelve bike formation, the road captain would thus signal his/her intention to change lanes, then wait till the last bike in his/her group--for example bike #6--moves out into the new lane, thus securing that lane. Then bikes #1 - #5 can safely move in front of bike #6. This is repeated independently with the second group, with the main objective being to safely shift all bikes into the new lane, regardless of any cars which may come in between the groups. As long as the groups are within sight of each other, no heroics by way of excessive speeds and/or more lane changes are necessary.
It's irritating to the group to have to stop 50 miles after everyone else has filled up to let one rider get gas. In other words, synchronize your fillups when team riding. Always start rides with a full tank.
Making a phone call, check out an interesting shop, take a picture, etc, can cause confusion. If you do pull over for personal reasons, wave the group on, then rejoin the formation at the next stop or at the final destination. Don't expect the whole group to stop and wait for you.
It doesn't always work out as planned, but that's life!