As with all games, there are things a person should never do or else all the fun gets sucked out of it for all participants. A great roleplayer can utilize any storyline and still have a good time without going beyond the basic rules that have been set. The explanations listed below are the absolute worst thing any roleplayer can either intentionally or unintentionally bring into any roleplay.
Powerplaying
Powerplaying is a roleplay term used to describe a situation where one person controls the actions of another person's character without permission. If your character is trying to do something to another character, any and all actions performed against a character that does not belong to you is always an attempt, even if they are innocent and playful. For example, if your character pushes another character down a hill, you cannot describe the other person's character rolling down that said hill.
You would setup the situation as this: Aren stepped closer to his companion and gave a devious grin, suddenly launching himself forward in a motion that would send Matthew rolling down the hill behind him if the boy could meet his mark.
It is now the owner of Matthew's turn to describe whether or not Aren missed or successfully pushed him down the hill. Powerplaying can be abused in any kind of situation and is most often seen in battle by causing harm to another person's character without asking permission. Attacks, just like Aren trying to push Matthew down the hill, are always attempts.
Godmoding-
Godmoding is most often used to describe a very powerful character. The definition is broad but basically is seen as someone who describes their character as unbeatable, powerful or being incredibly strong. In a roleplay situation, godmoding is when you roleplay a character who is ignoring the limitations of reality or a character that isn't often hurt, slowed down or effected by injuries or attacks that other people throw at them. While we're not telling you to hack off your character's limb, it is expected that your character should at least bleed and succumb to their injuries in a battle situation.
Godmoding can also be seen as powerplaying in certain situations. When a character in an impossible scenario suddenly defeats all enemies. Having limitless powers, ignoring flaws and realities or instantly healing is godmoding. It's when you portray your character as an all-powerful, unbeatable, super strong, or unstoppable character.
Subject: The Absolute Do-Nots of Roleplay 
