I love my LBS's group ride.
They've been doing the same route for years -- a cue sheet exists, but I've honestly never seen it. Newbs are encouraged to keep close to a more experienced rider. Folks who've been doing for years are like trail horses. They can do the route in their sleep and know the way back to the barn. It's very comforting to those of us who may fall of the back from time to time!
With about 80 riders on a good day, it breaks up into 3 groups:
A: about 22 mph average, no stopping, long route - populated by the hard-core racer types.
B: about 22 mph, 2 re-group points, long route - populated by the racer-types who like to chat.
C: about 18 mph, 1 re-group point, shorter route - populated by the women, older guys, and folks who REALLY like to chat!
So, the sum of it is:
Have different groups for different abilities/speeds
* Have a re-group point (ideally, at the top of a hill, which separates the crowd).
* Work on skill building where the route allows it - pacelines, hill climbing, etc.
* If your focus is fun and comraderie, vs. competition, be sure to stress it before each ride. Sometimes, the pack thing gets the best of some riders, and it turns into a competition. It's just the nature of the beast. It's a constant effort, I think, on our ride organizer's part to keep the intensity levels down. That said...a little competition on the hill before the re-group is sometimes a good thing!
Our ride starts and ends at the LBS, which is closed but serves as a staging area for the riders. There is a wonderful deli next door, and all are encouraged to stop by after the ride for coffee, bagels, etc. Lots of socialization during and after the ride.
That, I think, is a good group ride.