It has to be one of the hardest things to do in the whole photography game. I have spoken to several of my friends who do it and they had to learn the hard way, not necessarily taking bad photos, but being ill prepared.
The funniest/worst story I have heard was a friend who had all these wild ideas for shot ideas, he had scouted the location as well, so had found nice places to take photos and on the day it rained and not just rained, it RAINED!!! Then the family wern't behind his wild/fun ideas, so he had to rethink and everything on the spot.
He now has a checklist that he sends people, which include the style of photos they want from the day!
Group photos should be:
Traditional
Candid
Fun
Combinations
and so on.
Have you spoken to your photographer?