It's intense to shoot a wedding but I bet you'll do well! Go early and to the rehersals of you can. Get loads of photos of everything from the getting ready, the vows, any tears, the bride or groom hugging people in the wedding party, the cake untouched, the cake cutting, signing of the wedding license, throwing of the bouquet and group shots of the whole wedding party then split it into groups like the bride & groom with the parents, then with just the bridesmaids, then groomsmen, ask beforehand if there are any people specifically who you'll want pics of but really get everyone you can. Get some really romantic posed shots of the bride & groom too! I got the sweetest dip when I shot a wedding!

I suggest making a checklist ~ at least a mental one
Make sure your batteries are charged up and ready to go oh and check to be sure you have room on your memory card!!