In game terms, any expected or polite behavior which is not enforced by the game, GMs, EULA or TUA. If you break a rule of etiquette the worst that can happen is people won't like you, may kick you out of the group, won't want to group with you, and might ignore you.
The role-playing rules on RP servers are not etiquette as breaking them is punishable by a GM. However, some of the role-playing rules are based on etiquette.
Because punishing bad etiquette relies on the boor being ostracized and unable to find anyone to group with, his reputation must reach a high a percentage of the players in his faction as possible. With high server populations, a poor reputation may not spread as far and as fast. This means the tendency is, the lower the server population, the better the overall etiquette as more people know each other.
In general
- Don't repeatedly try to duel a character when they have declined.
- When you have finished playing and you are in an inn or a city, rather than going AFK and letting the client log you out automatically, do a kindness and log yourself out. This allows other players on high-population servers that are in queue to log in earlier. In logging off, to free up space for the next player to log in to that server, you should back out to the beginning log in screen where you type in your account information, or select another server.
- Do speak to someone before inviting them to a party.
In chat
- Use the proper channels (/1 for general chat, /2 for trade or WTB/WTS requests, /3 for LFG or LFM requests, etc.).
- Politely ask questions and politely offer answers.
- Don't use swear words, derogatory terms (except perhaps in jest), or L337-speak.
- Don't spam a channel.
- Don't ask for money at random.
In combat
- Understand your role (Nuke, Heal, Tank, Melee, Puller, or Scout).
- Don't train mobs, and avoid causing adds.
- Don't kill steal.
- Don't gank or grief.
- Don't bluewall.
In looting
- Establish Looting Rules before party gets underway to avoid confusion.
- Observe Need before Greed practices.
- If you wish to roll Need on an item, ask permission from your party members and let them come to a consensus BEFORE you select Need.
- Roll before looting a chest or container, and highest goes first. If you see a chest during combat, wait until combat is over before announcing your discovery and making your roll.
- Offer items you've looted that you can't use, but other party members can, such as:
- Don't ninja loot.
- As party leader, setting Loot Level to Master Looter without asking may be taken as an insult or as a way to ninja loot.