Bunch of things ...

If possible, learn the route ahead of time. Maybe try to take the car over the route. Some of these events are not well marked. Try to print or obtain a cue sheet in case you end up riding by yourself.

The start of these rides is often a madhouse. Riders will eventually spread out with people grouped by pace but, at the beginning, it can be crazy with very slow riders in the front, in the middle and all over the road. Ride defensively.

General pacing advice is to start a little easy and finish strong. Newer riders (or runners, or whatever) get caught up in the excitement and then have nothing left.

Define your personal objectives. Do you want your best possible time? If you meet friendly people who are going slowly, do you want to stay with them to cultivate some future riding partners? BF seems to attract its share of loners. I like to meet as many people as possible.

Are you riding or driving to the start? If you're driving, mount the bike on the car the night before. Put your helmet, pump, gloves, sunglasses and anything else you need in the car. Minimize "day of" activities as much as possible. Make sure you have pre-registration forms, ride t-shirt, pin-on number (and safety pins), checks, cash ... whatever.

Don't overtrain. Since this ride is longer than you're used to, don't ride the entire course too close to the actual ride date. Build in a couple of rest days if you do that. With a week to prepare, maybe try to add a few miles to or from (or both) work. Try a ten mile ride ... then a twelve ... then a fourteen. Just make sure you cut that back a bit for two or three days before the charity event.

These events can be great. Just have fun and be safe and don't worry about performance. You'll be a charity ride pro in no time.