Good etiquette in the field makes for a safer, more enjoyable hunt.
A good display of sportsmanship is not to out-load your partner. If you are both shooting doubleguns this is irrelevant. However, if you are a repeater operator and your buddy has a two-holer, just load two shots. Tell your two-shot toting friend you are doing this. If you are both using repeaters, establish how many rounds you will load. An even playing field is always appreciated. Make sure to always check the house rules at a club or plantation.
Basic, but sometimes overlooked, shootin' courtesies are essential for the safety of hunters and dogs alike. Be extra careful with dogs, particularly when they are not yours. Some folks do not like birds shot over their dogs unless the performance was perfect.
Shooting bumped birds or shooting after a dog breaks and is not steady can set the stage for poor dog behavior all day. Just communicate with the owner to find out his expectations and guidelines. Likewise, ask about ancillary game. It may be shunned upon to shoot woodcock, pheasant or rabbits. Of course it depends on the season but it also depends on who's land your hunting and what the dog owner allows.
Don't assume anything that may cause friction with your acquaintances.
If you happen to shoot a limit, quit. I know in some circles guys will keep shooting birds until they get a "collective limit," that is a limit for each regardless of who shot them. Bear in mind this may not be legal in some places. If you've got your limit in new company it is the most basic courtesy to help the hunt without expecting to shoot another shot. If a "collective limit" is legal and you are invited to continue by your hosts (or guest) decide based on the totality of the day's circumstances based on your perception.
Another often overlooked courtesy is to offer peace of mind to others when storing guns. You may be placing your gun in a horses scabbard, a wagon box or the truck. Regardless, I always show my chamber to another hunter and say "Empty gun." Everyone can enjoy peace of mind and the others develop more trust in you. Don't be embarrassed or hesitant to do this. It may sound trivial but believe me, it is much appreciated and says a lot about your character and sense of responsibility to people who don't know you well.
Back at the lodge, car, or gun rack never touch anyone else's gun without asking permission. Some folks get hinky about that. It may be a matter of superstition, skepticism or fear, but some people just don't want their guns touched. Once in a while it may be that the gun cost more than your kid's college tuition. Whatever the reason, you can never go wrong if you ask first.
Courtesy won't make you shoot better. It may make you get better shots and it could also lead to an opportunity to shoot more often. It will make your hunt safer and it will eliminate any regrets. Quail hunting is contagious. If you introduce someone to the sport they may become addicted. If you are a newcomer, I bet you will get the bug.
Courtesy is contagious too.