Alysia (my fiancee) and I went to see The Descent last night, and one aspect of the movie really surprised me.
It translated well to GMing, too: Focus on something unexpected, and enrich the game in the process.
I figured The Descent would be about things in the cave system eating the spelunkers — a monster movie, pretty much like The Cave — which it was. But they played up the claustrophobia brilliantly, which I wasn’t expecting at all. (The Cave didn’t do this, and it should have.)
I don’t get claustrophobic easily, and there were scenes in the movie that made me cringe. The caving was shot quite well, and it really ramped up the tension. The movie would have met my expectations without doing this at all — and by focusing on this element, it exceeded my expectations.
When you GM, look for these opportunities — chances to add more depth than your players might expect, or to focus on a secondary element of the adventure.
This can be unplanned, too, as long as you’re paying attention to what your players are interested in. If they like something more than you thought they would, run with it and see where it goes.