Here's the tip I didn't read - vary your poses!!! If you all stand the same way each time - they can get repetitive even if the background is different. Sit, stand, squat, stand square to the camera, stand at an angle, goofy poses, arms out, hands on hips, big smile, sunglasses on, sunglasses off, and don't worry about what your hair looks like! Some of the photographers will make suggestions, but others aren't as good - so you need to be prepared, too.
The less you worry about getting a good shot of the people in the photo, the more likely you will get a good one!