Lots of good info already. Add this in.
Before you shoot, determine the print sizes you will need, and then shape the group to fit the frame.
TWO PROBLEMS...
1/ it makes no sense to have a couple of wide rows, and lots of enmpty space above3 the people, and in the foreground in front of them. But if the print is going to be, say, 4 x 12 inches, you'll be OK.
2/ with 35mm film and most digital SLR cameras, the full frame enlarges to 8x12, not 8x10. So if you want 8x10 prints, make sure there
's empty space at the sides of the frame, so you can cut off two inches when making 8x10 prints.
Another advantage of shooting from up high is that the angles of the flash mean that the front row and back row are closer to the flash than when the flash is lower.
This matters in regard to falloff of the light from the front row to the back row.
The farther the flash is from the group, the less the falloff is. But, of course, the less light hits the group, too. So with big groups, lots of power is important.
And, of course, do you just want to line these folks up, or do you want to arrange them in some form... old guys in a group and young women in a group, or gold-winners in a group and silver-winners in a group, etc., etc.
Outdoors, be really careful of overhangs. I once spent hours retouching a photo someone had taken with the back row in the shande of a tree and the front row out in the daylight.
