I was an usher at a wedding once. The best man passed out during the ceremony a few minutes before he was supposed to give the groom the ring. The people in the front row saw him start to wobble so 2 of the guys got up and put an arm under each of his arms and carried him out. The guy on the video camera panned to the left so none of it was on film and when they got him to the back of the room, I took the ring out of his pocket and walked back up the aisle and stood in his place. The camera panned back right and all was well.
The funny thing was the bride and groom didn't know what happened until I handed the groom the ring. Oh and the guy that passed out was black so on the video it's like... what happened to the best man and who is that white guy !?!?!?
Best thing to do is know what the bride and groom want {after all it's their wedding}, stand up straight, look people in the eye and firmly but compassionately show them to their assigned seats. The rest is a cake walk.