Say NO to group shot killers. When you're the main photographer and trying to take a shot of a group, have you noticed that aunties and uncles and kids try to join you and take shots with their iphones or whatever cameras? When multiple photographers are shooting a group, people in the group will end up looking at different cameras and you won't have a single shot where all the eyes are looking at your camera.
If other "photographers" try to join you, you can do two things:
1. Get someone to organize a queue, so everybody can take a shot one at a time.
2. Stand out, and respectfully wait till the others are done (usually, when you do this, somebody will get the message and ask the other "photographers" to leave).
Oh...and make sure, you're not a group shot killer.