Yeah, the biggest thing is not to even have your camera out of the bag while they are making images that they set up and pose themselves. The bride and groom will probably sign a contract with some sort of provision that there will be no other photographers that will be makeing those images. Also doing so will seriously slow down the process and long portrait sessions before/after the ceremony will only serve to aggrivate the bride and groom. Candids, knock yourself out. Bridal party poses at the altar, et al. leave them alone. Cutting the cake, first dance, throwing the bouquet, knock yourself out. Just pay attention to where the photographer is and stay the heck out of their way. And have a ball.