I've shot a few weddings, but it's been years. I didn't enjoy it very much, but
one thing that made some of them far less stressful; an assistant or photo
director. In that case, it was my wife.
While I was setting up cameras, changing film, she was getting everyone
together, getting them posed for the next shot. It made things go a whole
lot smoother. We got all the shots the Bride & Groom wanted, with a minimum
of fuss.
Also, take at least 2 of each piece of gear you'll be using. Three would be
better. I can testify to how happy you'll feel when your camera stops working
for no reason you can understand, but you have a backup. Lenses don't
malfunction as much, but things happen. You can get by with another lens
but no camera body..you're toast! Flash/strobe units, almost as important
as the bodies.
And never eat or drink at the wedding reception. Particulary if you're getting well paid, and not just doing a family favor. It's bad form, and
sometimes, people who are paying, resent you eating their food. I've been
offered, but always politely refused. I'm there to work, and I looked more
professional that way. What if you miss a shot because you're eating cake?
Eat befor e you go. Even if the clients don't mind, you still look more professional not eating at the reception. At least that's my opinion.
Summary:
1. Always have backup gear, always. Don't even take the job if you don't
have at least two bodies, and two strobes, and two of your most used
lens. Three would be even better.
2. Use an assistant if at all possible, to organize the wedding party photos.
3. Don't eat or drink at the wedding reception.
And before the wedding, weeks before, if you've met with the Bride and groom, and established a list of shots/poses you know they want, it can
be most helpful. Believe me, it makes it easier.
Just my .02 worth.