When I was rude, my Mom would ask me if I left my manners at home. Usually, I would respond with a quick-witted retort that grounded me for the weekend. At the age of 22, I stopped back-talking to my Mom and realized my bad manners. It was like a wake up call. Then I learned that almost every aspect of human life has some sort of way-of-doing-things, or manners. Mountain biking is no different.
1) Ride only on trails where bikes are permitted. Obey all signs and trail closures.
2) Yield to equestrians. Horses can be badly spooked by bicyclists, so give them plenty of room. If horses are approaching you, stop alongside the trail until they pass. If horses are traveling in your direction and you need to pass them, call out politely to the rider and ask permission. If the horse and rider moves off the trail and the rider tells you it's okay, then pass.
3) Yield to hikers. Bikers travel much faster than hikers. Understand that you have the potential to scare the daylights out of hikers as you speed downhill around a curve and overtake them from behind, or race at them head-on. Make sure you give other trail users plenty of room, and keep your speed down when you are near them. If you see a hiker, slow down to a crawl, or even stop.
4) Be as friendly and polite as possible. Potential ill will can be eliminated by friendly greetings as you pass: "Hello, beautiful day today..." Always say thank you to other trail users for allowing you to pass.
5) Avoid riding on wet trails. Bike tires leave ruts in wet soil that accelerate erosion.
6) Riders going downhill should always yield to riders going uphill on narrow trails. Get out of their way so they can keep their momentum as they climb.