If you live in the Grand Rapids area, you can do some great practice rides on the WPT: start at Sand Lake and ride the unpaved trail north to Howard City (8 miles) or Morley (14 miles)  and back.  Work up to going to Big Rapids(29 miles) and back. If you can do that, you'll have no trouble on this ride! You can also find unpaved country roads or dirt trails in your area to ride. The longest section of unpaved trail currently is 29 miles, so aim for doing a similar distance on dirt before the ride.

If you register early and commit to the ride, it will be easier to get out and train. Proper training is the key to an enjoyable ride. Ask your friends and co-workers to support your ride with pledges. 

If you think you need new shoes, saddle, or other equipment for this ride, get it a few weeks ahead of time. Probably the worst thing you can do is try a new saddle or shoes just before any big ride. You need to let your body get used to new shoes or saddles, and you need to be comfortable operating equipment such as clip-in (clipless) pedals. I still remember the poor guy on the first year of this ride who bought and installed a new saddle the night before the ride. By Big Rapids he was sore, by Cadillac he was in a lot of pain. 

There are food stops about every 25 miles (about every 2 hours) where you can refill your water bottles, so make sure you are drinking plenty of water or sports drink during the ride. A good rule is take a drink every 15 minutes, even more often if you feel thirsty or start to feel leg cramps. 

This is not a race, but you certainly want to finish in a reasonable time. If you find yourself riding slower than expected, that's OK, just make sure you don't compound the problem with long breaks at the rest stops. You do want to use the food stops to get off the bike for a bit, stretch your muscles, refuel (eat) and rehydrate (drink and refill water bottles), maybe use the toilet, but don't sit around and let your legs stiffen up. It will just be that much harder and more painful to get going again. Except for the lunch break, aim for no more than 15 minutes at a rest stop. I recently read an article that recommended less than 10 minutes at a stop.

(just remember to include some dirt training in these plans)