To train, start at your current distance and increase by 5 - 10 miles per week. Don't over do it. If you can make it to 50 miles, you can do 80. But frankly, I like to do the full distance once in training just to increase my confidence. Your training should peak the week before the event. The week of, you should taper down and just stay loose. At this point, additional training won't do much good and could lead to injury. Over use injuries have ruined lots of rides. Certainly stay off the bike the day before. Pass the time by cleaning your bike, lubing your chain, etc.
Other advice- don't change anything on your bike two weeks from the ride. Don't eat or drink anything new during the event. Remember to pump your tires up to full pressure. Hydrate, hydrate, hydrate. Don't forget sunscreen. Most importantly, have fun!