I'm going to assume you have a well fitting, bike in good working order, with adequate gearing for the course (because that's obvious) and add do not do last minute changes or repairs without having a chance to ride the bike before the event.
1. Start out as slow as you can possibly stand, and then slow down some more.
2.. Drink and eat often and before you are thirsty or hungry.
2a. Eat and drink things you are used to, not new things you haven't tried.
3. Do not over dress, (Big fan of arm sleeves and a shell or vest that fits in a pocket)
4. Sunblock and lip balm are your friends.
5. Relax upper body and arms, and change hbar hand positions periodically
5a. Stand up every so often to change position and stretch some
5b. Look out for squirrels if riding in a pack or paceline (and don't get sucked into going with one that's too fast)
5c. Ride predictably, specially when passing or being passed.
6. Don't rush rest stops, but don't linger too long.
7. Do not "train" for the ride for 3-10 days, tapering off, and erring on the low side.