I often ride my mountain bike down a local mountain trail. This trail is multi-use, in that it is open to all: hikers, dog walkers, sometimes even horseback riders.
I see a lot of bad trail etiquette, and a lot of people who seem oblivious that there even is such a thing as trail etiquette.
The number one thing to remember is just common sense: those moving fastest yield to those moving slower. Just as its true on the street: cars yield to bikes, bikes yield to pedestrians, runners yield to walkers, and so on.
When in doubt, communicate with your fellow trail user. Say “Hi!”, let them know you’re approaching and when you are passing.
If you are hiking, and being passed by a mountain biker you may hear the term “one back” or “two back” from a biker which indicates that there are more riders in the group coming up behind the first rider.
If you’re the one being passed, maintain your line and allow the other trail user to move along.
Good trail etiquette allows everyone to share the trail together with minimal drama and hassle.