In response to a recent thread here... Google+ Post on Reading the Shadowrun 5th Edition GM Advice Chapter ... I came to describe my own method for creating RPG stories with a beginning, middle and end. I thought I would share it on my blog as well.
I like to have a traditional story arc for my games, with a beginning, middle and end. However, how I handle that is quite different than conceiving of the ending in advance. What I do is lay out the general back story, and main NPC characters, their motives, and resources. I roll them up even. And play them like a chess game in the background, regardless of what the Player Characters are doing. Even if the PCs don't interact with them, they still are executing their own plans and doing things. So, from the point of departure the back story is already in motion.
At that point I create a Beginning. This entails Role Playing with the Players their ordinary lives for a session. It could be "life in the village of Hamfest" and it describes the nature of the environment, sets up the histories of the PCs, and gives some clues and information regarding the bigger picture of the Back Story. So that's the beginning.
The adventure begins and this goes on for some time and is The Middle. During this phase I take note of the plot threads and keep a list of the important NPCs and/or clues they encounter. These each form plot threads. In any given Campaign I find Players will follow some plot threads and ignore or abandon others as they go. That's fine. It's free-form play, do what you think is best. Meanwhile in the background, or foreground as the case may be based on the Players choices, the Back Story marches on. Indications of this are peppered throughout the game. This forms the Middle phase.
Now for the End Game. At some point after a few months of play, if the Players haven't done so already, I begin to Wind Up the Plot Threads. I take note of the one or two that the Players feel is the most important. Note - they may have totally missed the crucial plot thread. That's ok. They'll find out in the end what it was (for example The King of Brawn invaded the Western Lands and destroyed the Barbarian Queen's capital city, and laid waste to the Jewel of the West). The PCs either are involved with that, or they selected other threads to follow. Whatever threads they touched, I begin tying up the loose ends of three or four of the more important ones (usually there are a half dozen or more loose ends by the End Of The Middle - it's ok to leave some mysteries for later Campaigns, or just let them float away).
To tie up loose ends I simply re-introduce NPCs or Plot Points that they encountered in the past but have forgotten about, or lost track of. I push at this point for Plot Resolutions. Did they find the girl who had the Rosery Beads that the old monk mentioned? Well, now they do - and she saw the Army of Brawn heading West. Did they investigate the tunnel beneath Oakenwold? Well, someone from there encounters them in a bar and explains that his own group investigated it, and found the Sword of the Western Sun there, and returned it to the Queen of the Western Lands. Etc. If a Campaign is 20 sessions of The Middle, I may have 4 sessions of The Beginning of the End.
Finally, there is a climactic End of the End where the main plot line gets tied up. They intercept King Brawn as he enters The Eagle Pass, and with a skillful bout of diplomacy, logic, and heartfelt pleading on behalf of the innocent Queen, cause him to change his mind. Or what have you. The Player Characters decide by their actions what the ending is. Could be good, could be horrible. But what makes it work is that The End has Come.
And then we go on to the next Campaign, usually, yes, after a break where I re-organize and plan for a new Campaign.
So, in no way do I determine in advance what the Ending will be. I let the play-flow determine that. My example shows a tie up where the Main Plot was resolved by the PCs in the end - but it could have just as easily been the case that the Players had no interest at all in the Queen of the West, and the End Game involved their tying up all the loose ends related to The Witches of Dunswick on the other side of the Kingdom. But the method stays the same. If that were the case, then at the very end I would mention, "And news comes to you as you're celebrating your victory over the Witches of Dunswick in the Green Owl Tavern, that the King of Brawn has returned from the West with his Army, having concluded a successful and glorious Campaign against the Rebel Queen of the Western Lands. * ahem * ... All hail the King!"