Since this is your first time doing this I would advise the following...
- Take a quick trip to the church or facility well ahead of time (weeks).
- Take some test shots under lighting conditions as close as possible to what you expect on the wedding day.
- Find out where the bride and groom will be getting ready and check out the lighting there as well.
- Look for interesting places inside the church and on the grounds for posing individual shots of the bride or groom as well as places suitable for couples shots and group shots. Take test photos there too.
- A helper is essential. You will not have time to round up people for photos and take them at the same time.
On the wedding day...
- Keep in mind that you are there more as a photographer than as a guest. You volunteered for this so act accordingly. Skip the toasts and the cake. You should be taking pictures, not eating and drinking. You can get your cake and punch after the bride and groom leave.
- Insure that everyone present knows that YOU are acting as the official photographer and are doing it as a wedding present for the couple. This will help make sure uncle Bob doesnt interfere toooooo much with your shots. Don't be pushy or rude but be firm. Enlist the help of the mother or father (of the bride for her family or friends and of the groom for his) if someone is too unreasonable.
- Take pictures of everything and everyone, lots of pictures. Back in the film days, this was a very expensive proposition but with digital you can shoot 2-3 times what a film-based photographer would without significant additional expense.
- Carry twice as many memory cards as you think you will need.
After the wedding...
- Download your shots to your computer as soon as possible. Download a second copy to a different hard drive.
- Download copies to at least 2 CDs or DVDs (I know this sounds paranoid but you cannot afford to lose these images)
- As you process each photo that will make it into the "album" add a very discrete signature and copyright mark. Just because you shot the wedding for free is no reason to give up your "ownership" or not take credit for the photos.
- Package your gift as professionally as possible. Make up a fancy CD/DVD label rather than just writing "Tim & Beth's Wedding" on it.
- You might want to consider asking the bride and groom not to distribute copies of the album CD willy-nilly. Consider making additional copies of it available to family and friends for a nominal fee. Your gift was to the bride and groom, not to all their friends and relatives.
Of course there are lots more to it, but these are the rules I lived by back when I was doing this for a living (except the digital parts).
Good luck!