Obviously no one is or can strictly enforce these rules, but in general, if you want to get along with other players and have a good role-playing experience, these are the rules you should follow. Feel free to add.

1. You only control yourself. Your character is your character. You can write whatever you want about him/her, regardless of how good or bad anyone else thinks it is. What you do NOT get to do is write or declare anything having to do with other characters, unless you have their express permission to do so. Don’t write about your “shared past” with another role-player, don’t emote that you've done something, followed by how someone else reacts to it, just write about YOUR character. How other people respond to what you do is up to them. This will result in things not always going exactly how you want them to, but remember – this is an MMO, which means it’s as much about others as it is you. You’re creating a shared, dynamic story; not static, single-player fan fiction. The only exception to this is within the framework of the game. For example, If you beat someone in PVP, it's fair to say "I've defeated you before."

2. Keep your character’s story consistent with your character’s power and abilities. To use COH as an example, I remember a few times playing with characters who backstories painted them as unstoppable demi-Gods who could stand point-blank in front of an h-bomb explosion without a scratch. I get that the idea of playing Superman can be fun, but if you’re trying to role-play, it’s going to be weird when, during your early levels, your unstoppable demigod gets punked by some street-thug with a gat. By the time I left COH, The Blue Fuse was extremely powerful, but what I did was I started him off as your average-level superhero. He had super-human speed and electrical powers, but that was about it. Then, as I leveled, I continued to write his story (I actually kept an in-character blog for him), and after things like the reactor TF, he would go through changes that amped-up his power levels; which was fine, because when he hit level 50, he really COULD stand in front of a massive gang of Hellion gangsters without much concern.

3. Don’t tie your character to other fiction. Obviously flat-out plagiarism is a no-no, but having your character jump from, say, the universe of Halo or Gears of War…trust me when I say it ultimately results in more problems than it’s worth. City of Titans already has a rich background to work with, and if that’s not enough for you, you can add your own original back-story, including an entire, original dimension that you came from if you want; so long as it’s actually yours.