For the player unfamiliar with MMORPG's the interactive aspect can be daunting.  There are rules that have developed over time by the players that established players have learned to live by.  Learning these rules and playing by them will earn you respect from the other players and will help bring you better acclaim within the community.  Most of these are not official rules, and thus can't get you booted from the game, but most are respected by the good players and those following them will more likely find good groups and good guilds.

• Don't be a Loot Hog.  In a good group loot methods and order are decided at the beginning.  If nothing is decided, then the default is always assumed to be the honor method, rolling for good items.  Loot should be shared equally amongst the group, and those who are getting more than their share will not be very popular.  In a pick up group, there are generally two ways of doing loot.  The first way, and probably the most popular one, is the honor method, with a roll for good items.  This requires restraint by all of the group members.  Basically, you keep track yourself of when you last looted and who else has looted and try to take just your percentage of the goods.  Plus, when a better than average item drops such as a magic item, the group rolls on it and the highest roller gets the item.  When playing in a group remember that the healer and caster need to stand back from the mob and are thus not right there to loot it when it dies, so take special note of whether they are getting their share.  The second way many groups loot is by alphabetical order.  When you use this method it is the job of the group leader to keep track of who gets the next loot and then you simply loot one after another.  You can decide whether to roll for good items or simply take the luck of the draw that you will get one on your turn.  A third way to loot is usually done amongst friends and not in a pick up group.  This is done by allocating one person to loot and then at the end of the night splitting up everything equally.  Remember, if you are constantly looting you will not be very popular, and the next time you try to group with someone you may find it harder.  You should always be aware of how often you are looting and how often other people in your group are looting in order to try to keep things as even as possible.
• The first person or group to a camp gets the camp.  This is pretty basic and applies to set camps rather than areas of wandering mobs.  If you get to a camp and a group or a solo player is already there hunting things, you should simply move on to another spot.  The group or person there has the right to that spot and controls who can hunt there.  It is very bad etiquette to start killing things in the camp without asking for permission first.  Doing so will definitely get you on someone's hate list.  There are lots of hunting areas in the game, and once someone claims one you should respect their claim.  If you went there to kill a specific spawn for a quest or a drop you need, ask the group or person if they are willing to let you have that kill.  If they don't need it, then it is good etiquette on their part to give it to you, but not necessarily give you the rest of the camp.  If they are also hunting that spawn, then you need to wait until they are done before stepping in.  Ideally, a solo working the camp would agree to let you join him and he would get the first loot of the item the mob drops and you would get the second loot.  With two people you will go twice as fast anyways.  If not, you need to just move on.  It is his camp.
• If someone is attacking something, don't attack it yourself.  This is similar to the rule on camps.  The first person or group to attack a mob has the right to kill it.  If you jump in and attack it after they start to fight, then you are kill stealing and this is not accepted by most players.  Kill stealers quickly gain bad reputations and often find themselves unable to get in groups later on.  Sometimes you will see a player who looks like he needs help and want to save him from being killed.  This is kind of tricky.  If a player needs help, he will generally ask for it.  If you think he needs help, then ask him.  Don't assume he wants you to come charging in and attack his mob.  Of course, help is always welcome in the manner of heals, buffs and other non-offensive spells, but actually attacking a mob that is engaged with someone costs him points and is not generally welcome.  Furthermore, if you do attack a mob on another player, by all means do not loot it.  Whoever engaged the mob first has the right to loot it, no matter who helped kill it, unless it was such a ridiculously higher level than him that he had no possible way of killing it on his own.  This is not a hard and fast rule.  In general, if you notice a player's health is significantly lower than the mob's and it seems clear he is not going to win the fight, you can usually attack it and kill it for him and get a grateful response for saving his life, but you will be surprised how often, even in that situation, the player will instead resent it and will ask you to stop stealing his kills.  Your best bet in a situation like that is to ask him if he wants help and when he says yes, wade in and attack the mob.  You don't want to be labeled a kill stealer.
• Ask a person if he wants to group with you before inviting him.  It is not considered polite to just click on a person and hit the invite button.  Most players want to know who is inviting them first and to consider their offer a bit before accepting. With the invite screen sitting there in front of them, they are not able to con you and see what level and class you are to figure out if they would want to join your group.  They also don't know if you are inviting them to duo or to join an existing group.  Also, in a battle the invite screen actually disrupts the battle and can put the player in danger.  Instead of hitting invite, use the tell command and ask them if they are interested first.  You will get far more groups that way.
• Do not loot corpses of mobs you didn't kill.  Yes the corpse has to have been sitting there for a bit before you were able to loot it, but it still isn't yours.  It may be that a group pulled a bunch of mobs and are still finishing them off and haven't gotten to the loot yet.  Looting these corpses is known as ninja looting and will gain you a bad reputation in a very short order.  If you truly believe that the person who killed the mob is not interested in looting it, try to figure out who did it and ask his permission to loot.  If you are not sure, you are really better off letting it decay.  A person who goes around looting other people's kill will soon find himself with very few friends in the game.
• Use shout only when necessary.  If you are talking to a particular person, use the tell command and send that message specifically to him.  If you are talking to your group use group chat.  If you are talking to friends, take it to a chat room.  Shout is meant for asking broad questions to the whole area, and should not be used unless no other form of communication is available.  Use shout to ask for help with a quest or directions, to announce that you are looking for a group or another member for your existing group, to auction items, or to say something of importance that you feel everyone in the area should know.  Don't use it to talk about the weather or anything out of game.  Take that to a tell or a chat room.  Definitely don't use it to talk to group members.  The group command is better for that anyways.  Many people find it very annoying to see their chat screen scrolling along with some other person's unnecessary conversation, so please be considerate.  Also, when you do shout something, just shout it once and let it go for a while.  Don't spam the channel by shouting it over and over again.  It's pretty unlikely that someone came into range in the 10 seconds since the past time you asked something that can now answer your question, but it's very likely that everyone else in the zone is getting annoyed with your chatter.
• Don't Beg.  Yes other players may have better stuff than you do, but begging is definitely looked down upon.  Do not ask someone for extra money or items.  You are likely to just get someone mad at you.  It is OK to ask politely once for a Spirit of Wolf or other buff from a player who is obviously not currently in a group or in need of all his power.  People in a group fighting should not be asked, since they obviously need all their resources for their group.  When you do ask, don't demand it.  Ask nicely.  If the person says no, then thank him and move on.  He may have been busy in chat or is planning on using a lot of power soon.  If you are polite, he may remember you and help you some time later, but you can be sure that if you treat him poorly he will never help you in the future.