RFisher said:
Ditto...with the caveat that I also do some prep work. I'm terrible at making up names on the fly, but very good at building stories on the fly. To mitigate this, I have usually have a list of names prepared, and sometimes a name and a profession. I usually don't detail NPC's unless I know for a fact that the PC's are going to interact heavily with (read: Kill) them. Some relevant stats (Bluff, Spot, whatever), but usually just a skeleton.
If we're running a pretty complex adventure, I might do some prep work and plan their "random" encounters. For me, random encounters are similar to the previous "caltrop" encounters. It could be anything from bad weather, to an information gathering opportunity, to an actual planned "random" combat encounter. I'll have a handful of these to direct, redirect or just give the PC's something to think about.
I, for one, prefer the on the fly method with only an overarching plot and some detailed antagonists ready for the PC's to jump in and make the story their own. This prevents me from scripting the antagonists actions and makes them more flexible when reacting to (or anticipating) the party's actions. I almost never use the 'all roads lead to Rome' model, since my players are masters at sniffing out that kind of manipulation. Though I do dove-tail plots on occasion.
