I like to have a "Sweep" rider picked before I leave... I expect that person to be the last rider. I don't like groups more than 5 to 6 riders... and I don't let anyone ride with me that isn't geared up, helmet/gloves/jacket/jeans at the minumum.
I have the route planned out, stopping points pointed out as well for everyone to regroup(map handed out). I let everyone know they are to ride their own ride... I ride at a pretty brisk pace, so faster riders may want to ride up front... slower to the rear. There are stopping points (again, reinforce this!) for everyone to regroup... no need to ride faster or ride anyway you are not comfortable with! If you are going to bail, let someone know... prefer it is done at a stopping point when we are all together as a group, this way nobody "goes missing". If someone wants to swap with Sweep, do so at stopping point.
Make sure and plan for hydration and refuels if this is going to be a long ride. Plan on refueling at every 100 miles or so, depending on bikes that are riding with you... good time to hydrate and potty breaks too.
Yes, I'm a harda$$ when I ride... I like to ride, don't really like to stop... I like at least 300 to 500 miles if I'm going on a ride like this.
Just a few of my thoughts... for others to pick at.