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There are a couple of members from here that I've ridden with enough and feel totally comfortable riding side-by-side with on straight sections of road.

But in general, especially in larger groups, it goes like this:
Staggered formation with a more experienced rider up front who knows the route we have planned, lesser experienced riders in the middle of the pack, and an experienced rider who also knows the route riding sweep.
There may be more than one experienced rider trailing the pack through the twisties sometimes though, since not everyone is comfortable with pushing their bike hard through corners, and not everyones bike handles the same here either.
Twisties are most definately done in single file fashion to allow the use of the entire lane, and it aids in seeing more of the road (and any obstacles) ahead.

Each planned stop (fuel, food, etc) along the ride route is discussed before leaving from the previous planned stop, that way you don't have anyone turning left at a crossroad when they should have turned right.
Having a time on when you want to be at any particular point in the route is nice, but it can cause riders to push their bikes and themselves to the point of being unsafe sometimes, which can totally ruin the day for everyone.
Keep a loose schedule on where you want to be at a particular time, but allow for variables - a rider having bike probs, an unplanned pee break, a rider turning wrong direction on road, etc.
The ride itself is meant to be fun and relaxing, so keeping the particulars loose and flexible relieves any feelings of stress.