This is vexing, because in high school I enjoyed DMing more than most other things. I don't think I'm alone here in saying that I'm pretty omnivorous in the things that I enjoy learning and the stuff that I've gotten good at over the years. DMing is one of the few activities that exercises all of it -- skills social, linguistic, creative, and mathematical, never mind a great deal of random accumulated knowledge -- and that furthermore demands that I be aware, present, and fully operational for any length of time. Particularly when I was in school, being repeatedly warned that I would find whatever fresh hell was waiting for me next year "challenging," and being repeatedly disappointed, this was a pretty vital as at least an occasional feature in my social and recreational life.
I've spent the last year threatening at least occasionally to quit DMing entirely, on the idea that I've grown out of it, or I've found other things to occupy my time, or maybe it just was never as fun as I thought. Fortunately or unfortunately, I find that I just can't quit thinking about the dang thing, so I appear to be stuck with it. So I've been trying to figure out a way to run games without allowing them to become a vehicle for anxiety, at least to the point of unpleasantness.
The trick seems to be -- based on some very limited success in the past few weeks -- as it is with many things, preparation. The best antidote for anxiety is confidence, and the best path to confidence is sufficient knowledge to support improvisation.
Which brings me back to my original point. When I say "what I want going into the game," I'm not talking about style or system or mood. When I say "preparation," I don't mean notes or characters or locations or any of the junk I've been writing up and thinking about and talking about for any of the games I've run in the past couple of years. What I mean is knowing two things:
1. Given where the last session ended (or the circumstances devised for the start of the game), what's a situation that will give the characters (and/or their players) and an interesting decision to make?
2. Given the range of likely or possible decisions that could be made, what's the next such situation likely after that? (And after that, and after that, and after that.)
In the second place, obviously, this means knowing the characters and the campaign in order to have a sort of feel for where things are likely to go, and to be able to come up with something even if and when the players don't match those expectations. This means knowing the who and the what of the situation in question well enough to make the situation feel "real" to me -- that is, to make the decision seem significant -- and knowing what information I need to communicate to the players to make it seem real to them.
As indicated in the title, this is pretty obvious. This, however, is what makes it important to me: It's important, it's necessary, and despite that I've been struggling with it, and a number of other issues that it implies and is implied by.