I did a lot of reading about wedding photography, although I haven't done one yet...
Batteries: make sure you have extra!
Memory card: read above!
Take many many pictures! The formal ones (make sure you don't forget anyone - make a list) and the surprise pictures.
Meet with your friend and ask if they have preferences as pictures - make a list.
Gorgeous pictures I have seen... bride getting ready, reflection in mirror, wedding dress on a hanger, the rings..
Some pictures may appear tacky but they may represent a lot to the bride.
Better take a few tacky pictures and have them say meh, than forget about taking them and have them say 'I would have liked to have this or that picture taken'
Remember, you can't redo a wedding..... well, not usually with the same person

For formal pictures that you take outside (preferably), look for nice architectural buildings in the area more than flat space with flowers.
Stones and stairs have a better impact than just flowers.. again I don't know what season it is for you...
Google wedding photographers and get 'inspired'!!Good luck!