Unclear on your statement. Are you shooting your first wedding or the first one in 16:9?
If you've already shot weddings in the past, there shouldn't be much difference in the content thats shot. It'll just look different in your monitor. You may need to frame your shot a bit different but no drastic changes I can think of.
If this is your first wedding shoot, keep extra batteries on hand, film the entire ceremony, (even if its the long Catholic ceremony). Become very friendly with the DJ. This is the person who executes the events such as the first dance, cutting of cake, garter toss, etc. The DJ will tell you when these events are about to take place so that your ready for them. Most weddings follow the same basic schedule. Ceremony, formal pictures, introduction, first dance, best mans toast, dinner, cutting of the cake, dancing, garter/bouquet toss, center piece give away, and more dancing. Again, the DJ will let you know when these events will happen.