Whenever you sit down to GM a game, you think about a few things, but do you ask the most obvious question: "What do I, as a player, want out of this game?" Because you're a player, Mr. GM! You're supposed to have fun. You are not beholden to the group for the type of fun you want to have. If anything, they're at your mercy, since you're the one who's directing the game. This isn't to say that you abuse this: it's a game, everyone needs to have agreement of some sort. But GM's sometimes forget they're players too. They just play a different role.
What role is that? Well, your chief role is that of arbiter. You are the the representation of the other side of the imagined dream-space, the laws of physics, you represent adversity. All other roles are secondary to this one, because without this one the vast majority of games fall apart. Yes, there are GM-less games. If you're reading this article you're obviously not playing one of those games, so arbiter is your chief role. Everything else is secondary in running the game, but no less important.
You'll notice that nowhere in the previous paragraph did I say that the GM made up the stories, that he put forward his own vision for a game, or even that he had anything to do with the story at all! But he does, doesn't he? Since the beginning of time the GM has something to do with guiding the game. We could go into why, but that's a bit beyond the scope and intent of the article. We're here to discuss how you want to be a part of the story your group will make. There are three basic extremes, each based upon the three things I'd talked about earlier. They're that of passive, active, and aggressive.
Passive: The Passive Extreme is fun because it allows the GM to sit back and just let the players do their thing. They don't really want to effect the shared dream-space more than they absolutely have to. Think of a drop of water: it falls into another body of water. What happens? The drop of water falls, and the laws of physics take over. This type of GM usually just makes sure that that drop of water's effects take place, but nothing more. You might stick your head in and take care of things every once in a while, but for the most part the GM has fun enforcing the natural consequences of actions. Dungeon World is an RPG that sets this up the best. The GM just prepares the fronts, throws them at players, and watches what they do. He then applies consequences based upon the player's actions more than any agenda he's got. The weakness of a Passive Extreme is that they often don't come up with an overarching plot, making the game meander.
Active: You don't sit back,you stick your nose in. Fail that Climbing check? The bishop whom you hate more than anyone else is at the top, and he helps you up. Now you have to deal with him. The Active GM has an idea, he wants to get his point across, he has a vision. While he does make sure that the natural gaming world gets enforced, he's far more interested in throwing his own two cents in. Usually these people come up with incredible plots and characters and want their players to experience what they came up with. Burning Wheel is the quintessential Active Extreme game. The weakness of the Active Extreme is that they are prone to rail-roading on the drop of a hat because they forget this isn't just their story, it's the everyone's.
Aggressive: We all know those GMs, don't we? The dicks. The ones who love to beat up their players. The GMs who, on failed checks, make the world go to hell in a hand-basket because they think it's fun. Yeah, that's not the type of GM I'm talking about. He's just a jerk, the perversion of this type. I'm talking about the GMs who openly tell you that they're out to get your characters. That your character is a piece in a wargame, and he is intent on winning. Notice that? He wants to win. He'll play by the rules (hopefully), and he's not a jerk, but you know he's out to get you. And that's fine, actually. As long as he's open about it, and the players are fine with the fact that this GM is so damn competitive that he wants to turn the story into an epic struggle in and of itself. Old-school Dungeons and Dragons is usually what we think of, but a more clear example is Burning Empires. The GM is out to win, and he is bound by the rules of the game, same as the players. Granted, the rules grant him different abilities, but that doesn't change the fact that the GM's open and stated goal is to kick the crap out of the players.
Now, the important thing to remember is that these are extremes. One is not likely to always want the same thing out of a different game. I know GMs who were playing it passive for a while all of a sudden become very aggressive. But can you "fit" into one of these extremes? Of course you do, otherwise everyone would be the same and it would be boring. So think about what you want out of the game, and how you get enjoyment out of it. It'll help you not only pick a game that'll help out your style, but it'll signal to the other players what you're in the mood for. And clear communication is always helpful.