Learn how to do the big group shot. You never know when you might need it.
This is a very short blog. I have very little actual advice to give about shooting group shots. My first piece of advice is to stop spending time fidgeting around with your gear! This was what we call a "grab shot". You throw out a suggestion and hope people respond. When they do (like these young ladies instantly snapping into a line up and throwing arms around their comrades) don't waste time fooling around with how you might compose or whether the exposure is "just" right. Just push the button a few times till they get bored and then move on. In the tradition of Zen Buddhism there is no "right" or "wrong" way to do something. Just decide and go.
My second piece of advice is to always take advantage of overcast days. Groups in full sun squint, are uncomfortable and the results are way too contrasty. If you can't wait for clouds look for shade.
My third and last piece of advice is to start with small groups and move your way up to the larger ones. Get a feel for being in charge and then come to grips with the fact that you'll never truly be in charge.
If there's no money on the table it's a hell of a lot more important to have fun.....and be in the fun....than it is to make everybody miserable getting the "perfect shot".