Excellent points, especially about using a tripod. The main benefit is that you'll need taking many nearly identical photos in order to get "the one" where everybody in the group is looking their best. Unless you've done this before, you'd be surprised how many shots it can take. Somebody's always looking away, blinking, has their head/hands etc. in a less than ideal position. Once everything is all set up as Darlene says, just shoot as many shots as you can in a very short amount of time.

Blankets or fabric to use as backdrops. If you are going to invest in one thing, I’d say go buy a few yards of the cheapest black stretch velvet you can find (use a coupon at Joanns!). Black velvet works really well as a backdrop because it doesn’t show wrinkles and generally shows up as solid black in photos. Otherwise, walk through the house looking for any blankets you might have. Blankets with lots of texture also do a good job hiding wrinkles, like this one:


Know ahead of time how formal the wedding will be, and how you fit into the event.  Some wedding photographers, like David Ziser, like to wear a suit to every wedding.  Other photographers think it is perfectly appropriate to wear slacks and a shirt.  Some female photographers wear a dress, and others wear jeans and a nice polo.  I wouldn't say that there is one right answer here, but it is worth thinking about