I will befriend my enemies. I will never confuse my character's objectives with my own; while my character is legitimately trying to put one over on the other characters on the realm, the players behind those characters are my partners in creating story, not my enemies. I will pay special attention to those who oppose my character's evil actions, keeping the lines of OOC communication always open and doing my part to foster goodwill so that we can all enjoy the game together.
I will start trouble. Story is driven by conflict, and conflict is created by villains. In playing a villain character, I embrace the responsibility to provide story and roleplay not just for myself and my guild, but for others and the realm as a whole. Keeping in mind my responsibilities to the community, I'll go about this respectfully and openly in an OOC capacity, creating schemes and events that provide opportunities for others to have fun interactions as well as myself.
I will lose. Not ALL the time; that would be boring. But it is a mainstay of fiction that the heroes win, and it is a mainstay of both GOOD fiction and getting along with people in general that nobody gets to win all the time. I will be willing to embrace defeat, when necessary, for this is an opportunity to shake my fist, proclaim “Next time!!” and further my own villainous story.
I will act for good reason. Acknowledging that “'cos I'm evil” is not a valid motivation for anything, I will consider my character's story and personality when beginning any nefarious scheme, and will be sure to always incorporate a point that furthers her or his story. All people, real or fictional, do things for what seem like good reasons to them; even the insane act with a consistent internal logic, though others may not see it as such. My character shall not run around causing random disruptions, but act in accordance with a cohesive narrative.
I will plan to the end. As creator of the conflict, and thus the story, I will remember that people depend on me to see events through; there is nothing more frustrating than a promising story that falls apart before its conclusion. My character's plots (and thus my stories) will have a planned beginning and end, which I will implement with OOC input from my victims/adversaries so that everyone can have fun, and I will plan conditions for victory, defeat, and stalemate. Above all, I will never engineer a situation where my opponents must destroy my character or be, themselves, destroyed (unless someone specifically wants a plot to help them kill off a character); these end with everyone unhappy.
I will play the game. I will remember at all times that my character's foes are my storytelling partners, and never use my character's villainy as an excuse to ruin their day. When I feel anger, aggression or any negative state that I wish to work out using my character, I will queue for a dungeon or battleground and slaughter colorful bits of data until the urge passes. I am not my character; I am not a villain. I will, in short, play nicely.