I've been DMing a game of my own for the last 6 months or so at RPGCrossing, and while I've been having a great time, it's become increasingly clear how important improvisation is. As an example, here's a synopsis of what I put together as the opening chapter of my game, which is set in the Nentir Vale.
....If you're one of my players, you might not want to read this. Pay no attention to the man behind the curtain, and all that. :)
My Anticipated Plan: River Rats Plague Lowtown Fallcrest
- Amara Azaer hires the PC's as adventurers to solve the problem of an extortion ring in Lowtown, Fallcrest (the default 4e starting town).
- PC's start poking around Lowtown near the Lower Quays, where a lot of the extortion has been happening. Get ambushed by gang members, who are simply trying to rob them.
- A shifter who spies on them during the battle sneaks away, and PC's follow him to the Bluffs on the other side of lowtown where they have a minion-filled battle outside the River Rat's hideout.
- PC's find incriminating evidence in one of the buildings at the bluffs linking them to Kelson of the Lucky Gnome Taphouse.
- PC's confront Kelson at Lucky Gnome, have a boss fight, win the day, save the town, and move on to bigger and better things.
What Went Wrong: The PC's Go Off the Rails
After receiving the quest, the PC's decide to bait the thugs by posing as a rival gang at the Lucky Gnome Taphouse.
Are you kidding me? The very first thing the PC's decide to do is go to the home of the Big Bad? This was a blast. Kelson, who was tending bar when the PC's showed up, made some great bluff rolls, and immediately began making plans to deal with the PC's once they arrived.
I also invented a new character, Arya, who was playing dice games (i.e. gambling) in the corner of the room. She was based on an enemy I'd already planned to feature in the first fight, but she never had any real personality or background before there was a need for her to populate the bar.
Springboarding off of something that one of the NPC's said about the gang potentially having infiltrated the Fallcrest Guard, the PC's took steps to entice crooked guards to show up. This included recruiting one of my PC's to spread word of a new gang operating in the area among the guard.
I hadn't thought this through when my NPC said it, but I was planning to throw a couple of guards into the final battle to justify that statement. The PC's really latched onto it, though. So, I instead opted to create a pair of crooked guards, which I named Horace and Jasper (Jasper was female, though), who promptly showed up at the bar and started harassing the PC's.
I was a little worried about whether it was too convenient that the players' plan would work so well. But if nothing else, it seemed like a good way to get them out of the bar once the crooked guards left. This actually worked brilliantly. The thief in the party immediately followed the guards to a safe house that I invented in Lowtown. After he was subsequently captured, the rest of the party followed, and I had my ambush battle.
I decided to try to lead the party back to the Lucky Gnome now, with Kelson heading off to the hideout near the bluffs to organize the gang's effort against this new thread.
Rather than head back to the Gnome, the party decided to send Jasper, who they'd captured, to entice her leader...who they had not yet identified as Kelson...to come to the safe house to parlay.
Little did the PC's know--though perhaps they should have guessed--but Kelson already knew what they were up to. Therefore, rather than show up to have a conversation, Kelson showed up with the full strength of his gang behind him to wipe out the PC's. This was a tough fight, but it ultimately resulted in Kelson (somewhat controversially...more on that some other time) fleeing once his gang was decimated.
I hadn't planned for the party to meet Kelson until they hit their third battle in the sequence, but the story demanded it. I also hadn't planned for him to escape, really, but I wanted to get the group out to the bluffs to get access to an optional sidequest that I wanted to be available to them.
Of course, given that they'd already fought Kelson, I needed a new threat at the bluffs. Therefore, as a means of linking them into the next bit of story, I grabbed an Iron Cicle Spy from the Threats to the Nentir Vale monster manual and placed her in the bluffs. Unbeknownst to me when I started, it turns out that Kelson was actually in cahoots with the Iron Circle! What a great segue, right?
I spent a lot of time planning, write out descriptions, etc, before the game began...and ended up doing almost everything differently. What began as a simple little sequence of three battles, with a loose story, became much more as we went. New NPC's emerged out of necessity, and entire links between plot points developed out of thin air. While there were some issues with execution here and there, on the whole it became a far more interesting experience than the thing that I'd originally planned. This improvement was a direct result of the players' contributions to the plot, and the reactions required on my end to make it work.
So, for all of my planning, the most useful bits that I came up with in advance were simply who the main bad guys were, and what specifically they'd been up to until the moment the campaign began. Everything else came down to playing my NPC's as they would behave, given their motivations and what they knew minute by minute. Fortunately, in a play by post format, I, as the DM, have the time to get my thoughts together so that I can zag when my players zig. Something like this would be a lot harder to pull off in real time at around a table!