I hope I'm not too late.
Excellent advice given so far. The good news is that you aren't actually writing the story yourself, you're just documenting the story that has already been written by the B&G. All you have to do is capture the story that is being told. This will hopefully take some pressure off of you.
Your goal should be to help "document the events" that are already planned. It would be nice if someone that wasn't at the wedding could look at your photos and feel like they were there.
So, of course you want to capture the B&G, and family and guests that were there. But, also try to capture the venue as well as all of those precious moments.
As I mentioned in another thread, I was a wedding videographer for a few years and the concept of capturing the wedding is very similar but with different equipment. Don't be bashful, you have to get in there and get the shots, walk right up where you need to be while still trying to be inconspicuous, don't worry about blocking other peoples view!
Talk to the other photographer and make a plan and work together. Speak with the hostess, band leader, or DJ to get a schedule of the events planned, and check back with them frequently to see how things are going and to find out what's coming up next.
Get some shots of the:
Bride getting ready
Arriving or leaving in the Limo
Ceremony, wedding party, walking down the aisle, first kiss, rings
Outside and inside of the church and/or hall.
Table set up and flowers of the venue.
Guests arriving and greeting each other.
Cocktail party
Family photos
B&G walking into reception together.
First dances B&G, parents with B&G etc.
Toasts & Speeches
Throwing the bouquet and/or garter ceremony if they do that.
Cutting and feeding each other the cake
Dancing shots/Band
Good Luck, I'm sure you'll do great
Rich