We hike for the enjoyment of it, either for leisure or for the physical fitness benefits, but nothing ruins a good hike like running into others who disobey the rules of the trail. I've put together a list of general rules. I strongly suggest adhering to them as often as possible.
1. Yield to right of way: Bikers yield to hikers and horses. Hikers yield to horses. Hikers going downhill yield to hikers going uphill.
The idea behind the right of way rules is that bikers are faster and can stop and start more easily so they yield to everyone. Horses are large and unpredictable so they always have the right of way. Hikers going downhill are on the easier path so they yield to uphill hikers. Do not try to squeeze past hikers on a narrow trail. Find a place to step aside.
A personal story: I was walking a paved trail that was wide enough for three people. Approaching me were three women engaged in quick, animated conversation. The women refused to break their 'row of three' and actually forced me to step off the trail onto muddy edges so they could hog the trail and continue their conversation. That was rude and unacceptable. The next loop around I looked down at my feet and pretended not to see them. I held my shoulder stiff and when the woman next to me wouldn't get off my side of the trail I allowed our shoulders to connect hard and she spun around in shock. I kept walking. The third time we came around she stepped over to her side of the trail without incident. Idiots can still be trained. :)
2. Stay on the trail. This is not just for the preservation of the terrain. It is for your safety.
3. Keep to the right.
4. Pass on the left and announce your attempt to pass.
5. If you are stopping to rest, move off the trail as much as possible to keep the path clear for other hikers.
6. Greet fellow hikers politely.
7. Groups of hikers yield to singles or pairs.
8. When hiking in groups, do not take over the left side of the trail, or if you do, be prepared to move back to the right quickly when other hikers approach.
9. Excessive noise is considered rude.
10. When yielding to horses, move as far off the trail as possible and stand quietly. This is for everyone's safety as horses may spook easily in unknown situations.
11. Do not leave markers on your hike. Do not cut trees or damage the wildlife in memory of your hike. Take photographs for memory's sake.
12. Pack it in/ Pack it out. It is disgusting to see empty water bottles, cigarette butts and food wrappers littering a lovely wilderness. You have to pack it in to enjoy it on the hike, it doesn't take any extra effort to pack it out.
13. Keep your dogs on a leash. No matter how sweet and wonderful your dog is, it is an animal with animal instincts. It is against the law to walk your dogs off leash in any national park. Even if you have a sweet dog, it cannot be controlled if it gets into a fight with a not so sweet dog. Not everyone loves dogs like you do and they don't want muddy paw prints on their shirts or to have to wipe slobber off their hands. As someone who's been chased down on a trail by aggressive animals who are 'normally very sweet' this is my biggest peve about hikers. Use your leash.