• Make sure your character has at least a few significant flaws.
• Make sure you have at least a few restrictions of positive/good things that your character may not do.
• Always make sure you know how your character feels at the current time.
• Type slowly, think before about your sentences. It is not an arcade game. This applies especially to elves.
• Use proper punctuation and no abbreviations (or smileys).
• Never go too far away from the "basic stereotypes" of your race/gender/guild/religion. If you do, make it matter and don't do it in more than one aspect. Don't pick weird combinations just to be different.
• Make sure that any interaction is enjoyable for others. Making your characters interesting for others is the essence of good RP.
• Don't fall into the trap of making someone your friend who shouldn't be. Everyone is not your friend.
• Make sure your character has a background with likes/dislikes, plus/minuses, etc and always follow that to 100%, even when you do not want to. It will be extremely rewarding in the end, trust me on that.
• Be prepared to have your "background" control your character to the extent where you make a mistake or lose. It's just as enjoyable as winning.
• Refrain from powergaming - it most likely kills the soul of your character. If not, it makes you very boring.
• Don't solve quests if your character has no reason to do that.
• Don't "discharge" tension/feuds too early. Tension is a good thing and it should be nurtured slowly. If you have knocked out your opponent, give him the pleasure of being RP'd with. If you have been knocked out, always give your opponent the pleasure of winning.
• Always blend in and be compatible with the lore of the world.
• Play each session like it was your last.
• Don't forget to emote while you are talking and always do it without making forcing assumptions on others.
• Never willfully break more than one of these principles unless you have a good substitute.

With this said, I have personally broken some of these on numerous occassions. Everyone was a newbie once. They are subjective, but I think they are a goal to strive for. They are not listed in any particular order and they are not complete or absolute truths - more like good hints/personal experiences from of mine on how to create yourself an interesting experience.

Please add your own words of wisdom below..! - poSarian