the DM must be the benevolent dictator of his or her game
After 19yrs of DMing I have come to the conclusion that the DM must be the benevolent dictator of his or her game. Not the players, not WotC, not anyone trumps the DM for only the DM has to consider HIS or HER entire campaign. The players have their one itty bitty, though important, character to worry about, WoTC has the bottom line and selling more books to worry about. I have my campaign to worry about and only I am on the most intimate terms with the setting at large.
I have certain unbreakable rules:
1.) I am fair and actually want the player to have fun and their PC to shine. However my rulings and house rules are generally non-negotiable except in rare instances where I encounter something I haven't yet had to rule on or the circumstances are radically different.
2.) Every character and character concept will be appropriate to the setting. If there are no Samurai on athas, you don't get to play one. There are no asian type monks on my Krynn(which there weren't until 3e) because the setting, for good or ill, does not have the cultural context for them no matter how hard they try to make them fit so as to be everything to all people.
3.) Names matter - You must choose a name that is appropriate either culturally or if it vicerally sounds right. Those who make up dumb names do so intentionally. Those who can't seem to get a good name for their character appreciate the help. You want to create tongue in cheek, comedy names there are more suitable tables for your style of gaming.
4.) No one has fun at the expense of another player. A smartass PC who is funny in character is one thing, another thing entirely is to single out one player and have fun at their expense. No PC on PC killings unless on the extemely rare instances there has been an in game feud that has been understood as such by the players themselves. General rule no PC killing of PCs or allied NPCs.
4.) My stories and settings are inspired by the workd of Tolkien, Howard, Martin, Cornwall, Weis and Hickman, Bradley and others ie. it is somewhat gritty high fantasy in which adult themes such a sexuality, really evil evil and humans running the gamit between the holy and the depraved. Characterization is important. Character intentions and motivations are important. If you ever try to role-play to the best of your ability you are greatly rewarded.
5.) We will have thrilling battles but there won't be mutliple combats every session unless the region and story supports this. XP is given for creativity and role-playing.
6.) Advancement is slower than canon, sorry that is just the way it is.
7.) My rules exist for a reason and I will happily explain the reason outside the session.
8.) The PCs are the good guys, the heroes. I don't allow evil except in side mini campaigns designed to highlight something going on in the setting. Neutral is allowed but you might find it hard to motivate your character because there isn't a guarantee of wealth or even financial reward for what the PCs do. There are other types of reward, doing the right thing because its the right thing, reputation, the ladies love a hero, honorifics, etc.
There are others I am certain but the point is that I am a fair, reasonable despot. I do what I do for the sake of verisimilitude, internal consistancy, the setting, the story, the characters and ultimately the fun of the player's and myself.