There is nothing worse than White Mountain "peanut butter mud." Do not use the trail if the mud starts peeling up onto your shoes, your bike wheels, or if you start sinking in. This causes trail damage that is very difficult to repair. Plus you'll get a massive build up on your shoes/bike and they'll weigh twice what they did at the beginning of your journey.
Pack it in Pack it Out
This should go without saying, but yeah. Don't leave trash on the trail or at the trailhead.
Who Yields to Who?
*Bikes yield to hikers and horses
* Hikers yield to horses.
*Horses yield to nobody.
Stay in Control
Keep your bike, dog(s) and kids in controlal and be alert and aware of the possibility of other trail users. And try to avoid skidding your turns. It sucks fixing erosion
Don't Shortcut Trails
Do not shorcut trails or switchbacks. Switchbacks and turns were specifically designed to avoid going directly up and down fall lines and to avoid soil erosion. If you are out in the woods having fun you are, by definition, not in a hurry. Take your time and enjoy!
Don't get lost
The main Buena Vista loop while marked, is rough unsustainable two-track and is seldom used. Mostly people come here to use the social trail singletrack network that has existed for almost 30 years. Until we make the social trails official with USFS, remember they are only sporadically marked. If you are new to the area, download Trailforks. All of the trails that will be recognized in the future are there and you can find your way around that way.