Partying is what a MMORPG is all about. If we wanted to play a one-player game, there might be other games more suitable. Partying is the best way to get to know someone, as far as the quality of their character:
- How well they act around others
- How well they learn new features
- How well they develop and learn and use tactics
In order to be the best you can be in a group, it is good to look at other classes to see what they can do for you, and to see what you can do for them that they can't do for themselves. Don't be afraid to ask someone for a benefit that they can offer you; and if you have something they might benefit from, give it to them.
First off, it is not entirely uncommon for first-time group members who had never met before to offer an enchantment (as it increases their skill, which benefits them). If you don't get such an offer, do not just expect them to respond affirmatively to a request.
All classes that can buff should buff everyone in their party. Some buffs require certain talents or reagents, so you shouldn't be surprised if someone doesn't have the buff you're looking for. Just remember to ask. Many players don't know the lengths of all your buffs, so you'll just have to remind the buffer. In the case of a paladin, where they can cast only one blessing on each character, you should ask the paladin for the particular blessing you want.
Many classes are hybrids and you can fill two different roles. Everyone should know what role they play in any given party, and also how to play that role well.
See the Instance Grouping Guide for information that is absolutely essential for going into dungeons with others. It is incredibly annoying when people do not follow the principles outlined in that article. Some people can be taught patience and such; others can't. You should do what you can to learn from experienced people (who are usually notable just from seeing how they speak and act) and teach others the same.
It is considered rude to invite somebody into a party, especially if they have not asked for a party, without first speaking with them. In many cases, however, it's obvious that you have a common goal. In these cases, you may get an invitation to join a party (but you should still not give one before speaking). Some instances of this is when you see the same character over and over in the area of a certain type of monster which is a quest monster or one that gives reputation. In this case, it is very beneficial to be in a group even if you don't help each other. The reason is that all members of the group get credit for killing each monster that the other one kills. However, if you're not immediately in the same area attacking the same clusters of monsters, it would be good to have free-for-all looting, or else a lot of loot would probably not be picked up by the others.
Another important reason to party up is that (probably) in every case, two together will be more than twice as effective at killing any given monster or set of monsters than the two separately. Synergy is very important in grouping. Two paladins can have two different auras which can be very beneficial; three is nice, too, but the rewards are greatly diminished at that point, because the group would receive a greater reward from another class. Two hunters can benefit each other in a similar manner as well, along with two warriors, and so on. But the greatest benefit of all is to have only one of each class. But it is not always easy to achieve such a grouping.
Looting and loot drops in World of Warcraft are fairly straightforward. If the corpse of a monster has gold sparkles on top of it, it means there's something on the corpse that you can loot. Once you loot a corpse, if you don't take everything off it, everyone else in your group will have the option to loot.
There are a few different looting types in parties that can be set by the party leader by right-clicking on his own portrait in the upper left. Two of these types are affected by the loot threshold, also set by the leader (the threshold can be set to uncommon, rare, or epic).
Money loot is always shared in a party regardless of loot type. However, if a party member is out of range when a monster is looted, they will not receive a share of any gold found on a corpse and will not be able to roll for any special items found.
In addition to the loot rules that can be set up to run automatically (see Looting), many groups have additional rules that they add in. Don't forget to decide them before starting!