This article is from the Misc Bicycles FAQs, by various authors.
If it's an organized ride, you may be lucky enough to find a small group
to try to ride with. Try to find other people who are riding your pace.
You should have determined a comfortable pace on your previous long rides.
It's very tempting to start out hard, with a rush of adrenaline and all
the other riders around, but try to ride at a steady pace that you can
maintain for the whole event. The ride will seem to go by faster with
company. When I meet new riders, I ask lots of questions and try to get
them to talk and establish a group. You can also help each other out
along the way, in case of mechanical problems or physical ones. You can
remind each other to eat and drink and encourage each other along the way.
One person suggesting finding an unsuspecting tandem to draft, which is
a very good idea, but I can tell you they aren't unsuspecting!
Try to take short breaks. Several shorts breaks will work better than
a few long ones. It's harder to start up after a long break. Try to
remember to stretch during these breaks, and while on the bike.