DO
- give credit to the Bride and Groom (your friend) for hiring a photographer. As much as you may disagree with their taste, there are probably good reasons why they hired someone else instead of you.
- they may want images presented and taken in the style of said hired photographer
- they may actually want you to enjoy yourself and be in the pictures rather than trying to snap them
- they may actually want you to be in pictures without a camera pose
- Take pictures of the setup poses from behind the photographers
- Try to have an awareness that if you're in a compromising position at the base of the B&G's feet trying to get a unique angle, there's a high chance you'll end up that way in the hired photographer's shot

DON't
- Jump in front of the hired photographers mid shoot and end up with your head and flash unit at the bottom of a wide angle shot
- Jump out of a 'whole wedding group shot' at the last minute so you can get your angle and be conspicuously absent from the final group shot
- Jump in the middle of the aisle as the bride is walking down because the photographer isn't there (he may actually be with the celebrant using a long lens)
- Practice shots for your upcoming trip to Peru at the expense of missing out your duties (like being MC!)
- Presume that your shots for facebook are going to be better than the hired photographer's
- Take pictures of the setup poses from in front of the photographers

These were some experiences on the weekend where there were mostly very good natured photographers in the audience, but two noticeable exceptions including the MC of all people! Feel free to add to the Do's and Dont's
A few years ago before we started shooting weddings, we were guilty as charged very frequently!