It's been almost twenty years since I did two RAGBRAi's, but I'm sure a lot of the following still applies:
* Train. Get you butt used to being in the saddle.
* The fun is along the way. It is not a race to the next overnight stop.
* Look at each day as a series of ten mile rides or whatever the distance is to the next town.
* Always meet at the first bar on the left unless it is on the right when riding into the next town.
* One or two beers at a stop give you energy. More than that usually sucked the energy out of me.
* Bloody Mary's are your friend in the morning.
* Hydrate. Have a water with each beer/cocktail you have.
* Plenty of sunscreen.
* Know some basic bicycle mechanics and be able to fix a flat.
* Practice defensive, courteous riding on the road. Not everyone can be as smart as we are.
* Don't be a hermit. Be prepared to meet a ton of wonderful people.
* You will be desensitized to using a Porta-potty. No matter what the condition.
I road with a bike club that hauled our crap from town to town, restocked the ice and coolers, etc. Best way to go IMO. Went back to work the week after RABGRAI and by 10:00 am I wanted a beer and pork chop. Withdrawal took a little while.