Follow davidfig's suggestion. Doing a small wedding won't help you that much for the bigger ones, because the scenarios are not the same, especially inside a church, if there is one. If you must be the only photographer, have more or a photojournalistic approach - just shoot everything making sure to vary angles, and positions, so your photos don't look like snapshots.
If you (can) use flash, practice bouncing the flash on nearby walls, and ceilings, using a white card back to the face to reduce or eliminate raccoon eyes (shadows under the eyes). I suspect you know your equipment and your flash, if not hit the books fast, and do some practice runs. Do some research on the Internet to get additional ideas on poses, and hit photographic wedding books at the local library.
There is always a first time for everbody. If you have the opportunity to assist an experienced wedding photographer, you'll save a lot of learning time.
Last note. It's always an additional risk to take wedding photos for family or friends. Family ties and friendships have been broken when photos of such an important event have been ruined. It's hard to forget, and forgive.