I tend not to write much about my approach to the nuts-and-bolts of PnP gaming on Monsters and Manuals, because, to be brutally honest, those sorts of posts (actual plays, DMing advice, thoughts on managing the game) are the ones I least enjoy reading on other blogs. But a couple of posts (namely this one and this one, the latter of which in particular is simply excellent) got me thinking about the subject today, so here I am, inflicting some of my 'thoughts' on you.
The first thing I want to say is this: DMing is a lot like teaching, and it's been my misfortune to have done a lot of teaching in my life - thankfully only to adults (both proper adults and undergraduates). When I say it's a lot like teaching, I don't mean for a second it's like lecturing in the sense of standing in front of a group of people and haranguing them, thus imparting knowledge. Rather, I mean that the skillset that a DM needs is quite a bit like the skillset of somebody leading a seminar or tutorial in an academic setting; you have to facilitate discussion/adventure, make sure that everybody in the class/group is getting a fair share of the limelight, arbitrate over disagreements or debates, and, finally, be the voice of authority when required. Usually, this requires taking a back seat, controlling the flow: your job is to a) pose problems, b) clarify, c) provide expert knowledge (you are the ultimate expert on your game) and d) demand answers and decisions.
This last bit - demanding decisions - is crucial to DMing, I think, and is all about timing and intuition.
Let's talk about group decisions first. A group of five people will rarely reach an agreement on a correct course of action, especially if they all have large opinions, so you as the DM have to judge when a group decision-making process has reached enough of a conclusion that everyone has had their say, so that nobody feels short-changed, while also preventing decision-making from going on forever and momentum being lost. When it comes to individual decisions, you have to make sure everybody is getting a roughly equal share of attention and having their questions answered without hogging the limelight, that everybody is getting an adequate amount of time to think things through without being an indecisive wet blanket, and that everybody is on the same hymn-sheet with respect to what exactly is happening and what they plan to do.
This is all requires intution, and is quite a fine art. Sometimes players have to be chivvied along: "Come on guys, I need an answer, what are you doing?" Sometimes shy players have to have the limelight thrust upon them: "Greg, you look like you want to say something." Sometimes you have to make sure the players remember certain facts that they appear to have forgotten (because they're not robots and they're just playing a game): "Don't forget that you left all your rope at the cave entrance." Sometimes, you have to be firm, "No, you can't do all that in one turn." All of this requires a good sense of timing, an understanding of the rhythm and flow of human conversation and interaction, and a neutral but benevolent attitude. None of this can be learned from blog posts. To a large extent you either have it or you don't, but you also get better at it the more you practice.
The second thing I want to say is: as the DM you are the alpha male - even if you are a woman. Again, I need to clarifiy here that I don't mean this requires you to be dominant, to boss people round, or to act like a dick. But what it does mean is that everything flows from you: you set the tone. If you're feeling down, or bored, or a bit under the weather, then this is a very good indicator that the entire session is going to feel down, boring, or a bit under the weather. Likewise, if you're in the zone and you're feeling good about yourself and gaming in general, you can be sure this will generate a buzz among the players and get them having fun and being energised. What this means is that from the moment you walk into the room where you're DMing, you have to force yourself to feel good and energetic, even if you don't. (Again, this is what a teacher, or at least a good teacher, has to do, too.) You have to exude confidence and enjoyment about the game, because if you don't it will fall flat. I say again - you set the tone. I also say again - you can't learn how to do this from blog posts, but you can get better at it over time.
The upshot of all of this is that being a good DM, and thus facilitating good gaming, is in my opinion almost entirely a matter of feeling. Of course, prep is important, being able to think on the fly is important, and knowing the rules is important. But really, lacking one or even all of those things is forgivable if you manage to set the tone well and facilitate/control/arbitrate effectively. And conversely, if you don't manage to achieve that, there's a good chance the game will fall flat - no matter how well you've prepped, no matter how good you are at improvising, and no matter how many random generators you've got.