These are the most important and immutable rules of MET, the ones that keep your game and your players safe from folks who either don't care that you're playing a game or who take the game way too seriously. Always adhering to these rules will also keep your game amenable to law enforcement and other non-player folks.
No Touching. No Stunts
That means none whatsoever. It's far too easy for things to get out hand in the heat of the moment. Save the stunts for your imagination. If you can imagine you're a nine-foot-tall hairy monster, then you can sure imagine you're swinging on a chandelier or leaping across rooftops.
No matter how careful you are. Whether it's to prevent some fool from skewering himself on your new dagger or to make sure the police don't think you're a threat, weapons of any sort are forbidden. Even fake or toy weapons, trained attack gerbils or laser pens are not allowed. Use item cards instead.
No Drugs or Drinking
Well, duh. Drinking and drugs do not inspire peak performance, and players who are so impaired are a threat to other players and the game. It’s one thing to play a character that is drunk or stoned, but another thing entirely too actually come to a game under the influence. At best it's tasteless; at worst it's illegal. Don't do it.
It's Only a Game
If a character dies, if a plot falls apart, if a rival gets the upper hand, it's just a game. You and the rest of the players are doing this for fun. Taking things too seriously or taking character issues into real life, will only spoil everyone's enjoyment, including yours. Remember, playing a game should be fun. If you're not having fun, it's time for a reassessment.
Remember to leave the game behind when the session's over. “Soft” role-playing (conversing in character without challenges) can be fun, and there's nothing wrong with talking about the game afterward at the local diner. On the other hand, demanding weekly tribe meetings or trying to rouse your elder to talk business at three in the morning signifies the need for a change in perspective.
Be Mindful of Others
Not everyone around you is playing the game. You want to ensure that your game and your players are welcomed. Frightening people and getting the local law enforcement called on you is not the way to do it. This is especially true if you're playing in a public area, such as a park. It can be a very good idea to alert local merchants and police before you play so they're prepared. If you get curiosity-seekers, try to have some business cards on hand and offer to speak with them when you have more time.
Do What Works for You
We at White Wolf often call this proviso “the golden rule.” your game may have special circumstances that require a few extra bells and whistles to the rules, or your troupe may find a way to handle something that works better for you. So long as people are having fun, go ahead and run with it – it's your game.
Likewise, if you see something that you want in your game that doesn't appear with an MET system, then sit down and cobble up something that will work for you. If MET is all about telling stories, then here's the part where the Storyteller improvises.
Not “Win.” Not “Go out and conquer everyone else.” Just have fun because in MET it's not about how the game ends but what happens along the way.