Many MMORPGs have their own codes of etiquette while playing. These are expected since some games have communities that number in the millions. Any sociologist would note that there will be forms of norms, customs, and etiquette that will develop with such large numbers. While your game might have specific things not listed here, these are some general rules to keep in mind.
Be nice like you would to people in real life. Yes, it’s a video game but you are also playing with real people. Common courtesy can pay out in the long run as you have more people that will want to play with you in the game.
Don’t steal mobs from other players. If you are questing in an area and there are plenty to share, don’t go after the same one that another player is approaching. Some classes in the game might not be able to tag a mob as quickly making it frustrating when they are taken. Try to respect the other players in the area and do what you can do to share things if you can.
Ask and offer help before helping someone. At times the low level character might want a challenge instead of a high level player finishing off the enemy they are trying to fight. Be sure that the player really wants help before you intervene.
Don’t spam the chat channels with the same message. Say what you need to say or ask your question and wait. It may take a bit of time for someone to respond and saying it 50 times in a row doesn’t speed up the process.
Ask and never demand things from other players. Many times players want everyone else to do it their way. You need to ask other players nicely instead of giving out orders. Remember there are real people behind those other characters.