I think the most important rule to remember is to respect the other angler's space. As to how much space that is, a good rule of thumb is twice as far as you think. On a small stream it might be as far as a mile or more. On a big river 100 feet is good. Unreasonable you say? Bull! Move to the next pool, or down to the riffle leading out of the pool. Distance can be your greatest ally on a stream. That big famous pool with thirty guys beating the water chasing the 10 rising fish, pales when compared to the empty pool with only one or two risers.
If after that long drive, and longer hike you find someone fishing the pool you came all this way to fish, feel free to be disappointed, but do not feel free to wade in. If you are determined to work that favorite stretch, sit on shore and wait till the other guy is done. Better yet go elsewhere.
If some ignorant clod comes into the pool you're working; Explain to him, politely the error of his ways. If that fails and he (or she) decides their fishing is more important than yours. Do not stoop to their level. Hard as it seems, I recommend you move on. First you're less likely to catch anything with a bozo (or bozette) like that in the pool. Second the stress of having to be around this kind of clod is not worth the trouble.
If you're working your way downstream and come across someone working upstream, yield to the angler working upstream. This is an old rule from the time of Hewitt and Gordon.
If you are working your way upstream, and come across someone working upstream only slower than you, get out of the water before entering their pool. Walk at least as far as you could fish in half an hour upstream. Give them plenty of undisturbed water to work. If you know, tell them how far up you expect to go. "I'll leave the water up to the old fence row to you." That way they cannot blame you for not having caught anything. They might also let you know if twenty other guys just traipsed through. They might be on their way out and tell you to go ahead and put in.
In the event you find yourself sharing a pool with one or more anglers, give yield to anyone fighting a fish.
Do not laugh at casting flubs, unless they are your own. Never second guess another angler's selection of fly.
Avoid using the stream as a path. Walk from pool to pool on the bank. Leave a pool as quietly as you entered it. This means the pool needs less rest for the next angler that comes to it, if you are lucky it may be you.
If you see someone working a fish, or waiting one out, give them a wide berth, preferably by going to the next pool.
Talking to another angler is acceptable, and quite proper.
Not talking to another angler is acceptable, and quite proper.
Do not litter, and do not tolerate litter around you. Pick it up. If you smoke, take your matches and your butts out with you. Forest fires should happen on their own not with your help, so pay attention.
Respect fences, leave gates the way you found them, close the ones you opened and leave the open ones open.
Show the same respect to spin fishers as you do to fly fishers. Elitism has no place on our rivers. If you really think fly fishers are better, prove it by living up to a higher standard not by expecting less of others.
Offer advice only if asked, ask only if willing to listen.
No trespassing means no trespassing. If you really want to fish there, ask permission. You will be surprised how many folks say yes. But NO means NO.
Cellular phones, radios and television have no place on the river.
Be especially mindful of your manners and language around youngsters. They learn best by example.
Swearing, farting and burping are at the discretion of the angler, and quite acceptable. (Note previous rule.)
Lying is still acceptable, even expected, if asked how you did, or where you were. Lying about the hatch is not as decorous, but tolerated. Lying about your residency is illegal when purchasing a license. Lying in the grass and taking a nap is one of life's great joys.
Never interrupt a lying fisherman.
Enjoy yourself, but not at the expense of someone else's enjoyment.
Catch and Release.