Most of us have all had the experience of running an improvised adventure. Back in the day we called them "random". Although personally I never liked that term. Even though there were hordes of random generation charts for adventure creation that could be used for just such a game. In fact the game was really designed for creative spontaneity of several sorts, in spite of where we might have taken it. That was evidently the way it was done in the original playtests. At any rate we probably have all come to a gaming session unprepared to DM beyond the merest hint of an idea, and maybe not even that.
The game may have flopped, and it may have been a smash hit. One of the remarkable things about this game is that it continues to surprise us at every turn. We are constantly being challenged on an intellectual and creative level by the things that come up within the game. At times it is a player doing something original or at least unexpected. At times it is the story flowing out of us like it was meant to be. Events align just right and we find ourselves coming up with things we never would have imagined on our own. It's one of the reasons I love this game.
So in a way the game is designed for improvisation. Embrace it fully. It is the nature of vehicle in which we play. Don't feel bad if your thoughts or the direction of the game goes differently than what you may or may not have had planned. If players wander off the edge of the map then make it up as you go. Embrace the possibilities this presents. And don't be afraid to come up with new mechanics or new rules, new monsters, new and unexpected twists and events. Things that color outside the lines so to speak. The thing about roleplaying in the games we play is that they were not designed to be driven by a pregenerated story. The game doesn't work that way. Embrace this fact and let the story unfold itself.
This sort of opportunism is essential to allowing the game to reach it's full potential. In the storytelling medium storytellers had stories that they told again and again. They were largely memorized. But the thing we often don't realize it that they were never memorized verbatim. They weren't scripted and they weren't like a Greek play or a Shakespearean drama. Storytellers memorized elements. Outlines. The basic facts of a story. And when they stood in front of the fire, or took the stage, they had to read their audience. They had to adapt the story to the time and the people they told it to.
Homer's Illiad worked exactly this way. The outline of the story we have finally written down had been preserved for ages in the minds of storytellers. It only became concretized when Homer wrote in down. Now when we think of Illiad we often think of Homer's telling. But the outline of the Illiad had been used by writers throughout time. The elements of the outline are preserved in telling a new rewritten tale, that though it contains the same elements is essentially a new story. Shakespeare's works have been rich fields for exactly such creations throughout time.
So are our truly great modules and adventures published by the genuinely creative designers, also templates which we use to write our own stories upon. The story you tell when you use an adventure or make your own or go completely random. Is not generated by the elements themselves. The true story the real interaction is between the PCs and the GM controlled and generated environment. Relying on preprinted materials is fine, I'm not saying you shouldn't do it that way. But don't set yourself up for some sort of scripted story. The PCs are walking into a preexisting situation. How they react and what they do may be very different from what you expect. Embrace this and be prepared to run with it.
This sort of opportunistic GMing must be cultivated as a quick thinking approach to player action. The players present you with something unexpected, or are the direction of the game is not going in the way you had anticipated. Fine. Don't think about what you had anticipated or planned or expected. Think instead about what the players are doing. You know the world around you. You have read the module or prepared the city, kingdom, dungeon or wilderness ahead of time. Or maybe you don't and your making it up as you go--even better! Consider the players' actions as fuel for what happens next. Think about the natural and at times unnatural consequences of their actions. And make it happen.
Say for example you had planned for the PCs to rescue a Princess kidnapped by an Ogre Mage. You hadn't really planned much beyond making a quick map of the Ogre Mage's caves. The adventure starts with the PCs being summoned by the King. The PCs arrive and you give in your best imitation of kingly speech an impassioned plea for their aide and offer a royal reward to boot. But the players aren't impressed. And though they reluctantly agree to the quest they quickly get sidetracked in the town visiting the local tavern. As a GM you have no idea why they are visiting the tavern, or avoiding the quest, despite several reminders that they king expects them to get underway immediately. To no avail however as they begin to seek out a local apothecary to see if they can purchase some poison--goodness isn't one of their alignment foci. So, what do you do?
Now right off the top of my head I see several possibilities. First poison is a controlled substance in this town. And when they get to the apothecary, a tall thin man with weasely features named Arndt, and ask for the black stuff, Arndt gives them the local thieves sign to see if they can identify themselves as such. Of course they can't, as the sign is known only to local thieves and assassins. This makes him suspicious and he says he doesn't carry the stuff. But if they come back at sundown he can have some brewed. Unknowingly to them Arndt is playing both sides of the street. As soon as the PCs leave he notifies the authorities to be ready at his place to arrest the ne'erdo wells. Of course Arndt extracts a fee from the constable for the information. And then Arndt promptly notifies the thieves and assassins guild--Thee Humble Cutters they call themselves, as the front for their business is a rather unprosperous harvesters union. And Arndt makes it clear to his under the counter regulars that there are unauthorized assassins operating in the region.
Three days later as the party is trying to break two of their number out of the dungeon while dodging assassination attempts by the Cutters, they catch a conversation by some guards that the Princess Marroway has evidently been sold to some adventurers from the south where slavery is common. (Actually this was my second choice. I wanted to have the Ogre Mage sacrifice her as a material component in an evil spell, but this way there is now a whole other adventure hook to the south.) And if the party doesn't realize that they are going to get framed for the slave trafficking, I simply let them hear the guards add that the King is sure the dastards who he hired to save thee princess were evidently slavers.
Mean? Cruel? Evil? Maybe, but that is the world the PCs live in. I'm certainly not railroading them. They chose to enter a rather seedy and dangerous underbelly of the kingdom and are now caught up in it. Evidently that was what they wanted. So instead of the Ogre Mage's hobgoblin minions, they are now facing the Cutters and Kingly Justice. Ouch. Ah well. Such is the nature of improvisational play. The story happens because you are willing to take advantage of opportunities. Fortunately you have longer than the 5 minutes it took me to write this in actual game play. Your mind is churning and working the whole time. Take the opportunities the players give you and weave the story as you go.
This is Improvisational Ability. Opportunism in game related storytelling. Don't be afraid of it. Cultivate it and use it to it's full potential.