Here are some common rules of RPG.1.Know the ruleset - All roleplaying games and situations should have clearly defined rules and parameters that the participants must follow. Defining an adequate ruleset is the responsibility of the organizer and is the first important step to creating a successful RP situation. These rules can be anything from as simple restricting the time and place of the rpg (i.e. midievil england sits shouldn't have jedi knights running around in them) to extremely complex rules such as how attacking damage is scored.
The important point here is that you, as a roleplayer, should know the constraints placed upon you before you start playing the game. This is less important in a single player situation, but when your actions affect other players as well, your knowledge of the rules can greatly affect their gaming situation as well.
2.Listen to the Moderator/Game Master - When you're a student being graded by a professor on your knowledge of a roleplaying situation this is probably quite easy for you!
When it's for recreation sometimes it's easier the point gets a little less clear. It shouldn't however.
It is important for the game moderator to have control over the rules and to continue to modify the game as it takes place. A good moderator will know how much "moderating" is enough and won't step over the line. Games do however tend to evolve over time as new scenarios occur or things happen that weren't originally anticipated. The result is that to keep the game running smoothly, the gamemaster does does need to play direct role and at times change the rules.
What players should remember is that the game in many ways belongs to the gamemaster, in the case of disagreements, they should be voiced outside of the game itself. If things are not reconcilable, then the player should respectfully leave the game (quite possible to create their own with the desired changes).
3.Be polite - While this probably goes without saying, treating other players with respect is something that should always be done. Unless of course disrespect is something that is involved in the story line. The point is, treat the player themselves (possibly not the character) the same way you would like to be treated yourself.
(Rules found at-http://www.roleplay.org/articles/rpg-rules/)
NOW FOR ME TO ADD MY OWN*No god-modding.
*No cybering.
*No taking total control of the RPG!
*No Mary-Sues, unless the RP permits.