3. Put real world races or religious groups into your game and either subjugate or disenfranchise them. I would suggest playing a colonialism setting with mature players only, as it can get very racist very quickly and might be awkward and off putting for players (especially minorities).
12. Encourage inter-party conflict, especially if you keep secrets. Help all of your players screw each other over.
13. Bring a God NPC into the game, played by you. You have to protect your story after all, it is far more important than letting your players run around with no direction. Make sure your NPC is stronger than all the other PC's in every area of the game, and gets some cool unique magic items.
Let the party break up as often as you can and promote individual side-quests like the thief sneaking off in the night to try to steal from someone not related to the quest. Make sure it takes at least an hour away from the other players.
Along the same line- let the thief steal from other party members. This is a sure-fire way to have hours of fun!
15. Never accept any player input on where he or she wants their character's arc to go in the game. Instead try to force their character into your vision for your gameworld, even if what you want is the opposite of what the player wants.