Endurance riding is a discipline I've never explored and I'm very interested. I have a horse that I think would be exceptionally well suited to it but all I really know about it is what I found on google.
I'm a horse & dog trainer. Spirit Dance is a 7yr old reg Paint stallion. He's western trained and although he has been bred he is able to behave himself reasonably well around other horses. He's got heart, attitude and stamina... he loves exploring and adventuring and he's built like a really big mountain pony. :P
Find an endurance ride in your area (aerc.org has listings of rides by regions), then go as a spectator. Wander around, talk to people, watch the vetting process, sit in on the official Ride Briefing - especially the New Rider briefing (which all rides offer after the regular briefing) - and soak up the atmosphere of the Ridecamp in it's totality. If you can look around with a smile and think "this is for me!", then you're already halfway there!
Now go home, reread the AERC rulebook and the links posted above, then lay out a 90 day course of distance training for you and your horse (the "How to Do Endurance" link at olddominionrides.org is the BEST for designing your training program to meet your horse's needs AND getting you ready as well with everything you'll need). Get together your corral containment equipment and teach your horse to respect it.
At the end of your initial training period sign up for a ride (Limited Distance)...and go enjoy the day.
I echo all the above sentiments, and I just started endurance riding this year. I volunteered, read everything I could get my hands on (love the Old Dominion info, maybe get the new Endurance 101 book), and very early on started training my horse. Since I wanted to make sure he'd be a good trail horse and hold up for years (hopefully!), we did a long time of long, slow distance. And horse camping. And riding with others.
It also helps to have a mentor, or at least someone local you can ask questions of. Setting up my trailer has been pretty fun, teaching the horse about the high-tie, lots of things that aren't riding. It's been pretty fun so far, I started with a 25 LD and then 2 50s. And learned A LOT! Though I'll never do very many rides a year (finances, other interests) I am very glad to have gotten started in the sport. Good luck!
"Do your best, and leave the rest, twill all come right, some day or night" -Black Beauty
Definitely read through all those links. We didn't volunteer before our first ride. Just got the horses ready (they were already good trail/campers so just got them fit) and went. Showed up, said we're new and ride management was fantastic about running through the whole process with us. Go vet in here first. Meet here. Go there next. Etc. We decided to start at the very end of the pack just to stay out of everyone else's way. It worked out well. We did end up passing several people, but starting at the back kept the horses calm.
Endurance is a whole lot of fun. Everyone we've encountered has been very nice and helpful. Most people are pretty willing to point the new kids in the right direction.
I've been "doing" endurance rides for 2 years now. I went online, read all the training and feeding articles I could find. I found a mentor and rode with her for a few training rides and for my first ride. I am totally hooked! It would never hurt to volunteer at a ride beforehand, I just never did it. Get your horse conditioned and jump in! I highly recommend a mentor for your first ride.
I rode novice rides when starting out, I learned a lot on them!