Quests

Any long form story, aside from a slice of life piece, is going to be about a quest. So, what's a quest.

A quest is a mission that is completed by doing several other missions. In the classic story, the hero wants to kill the villain. That's the main quest. So now the hero has to complete it by doing smaller missions. The first mission is to find out where he lives. The second mission is to go there.

Now, since a quest is made up of missions, you can realize that each mission can consist of smaller missions. Our hero has the simple mission of going to where the villain lives. But on the way, he sees a platoon of guards protecting it, so he now has the sub-mission of evading the guards. After completing the sub-mission of evading the guards, the hero completes the regular mission of getting to where te villain lives. Now he's at the third mission where he has to find and kill the villain.

Another aspect of quests is that they are malleable. Just because a main quest started with a particular mission doesn't mean that it has to stay that way. When our hero finds the villain, he has the obligatry speech before delivering the coups de grace. During this speech, he finds out that the villain was not really a villain at all. He was framed by the person who really did it and was too afraid to come clean. Now the main quest has been altered to go and find this new person and kill him.

As the main quest itself can be altered, so too can it be extended. Our hero finds this new man and kills him, thus ending his quest. But in doing so, he is unfulfilled. He cannot understand what drove the villain to do the things he did. They didn't seem random, but they had no obvious purpose. The hero now starts a new quest of finding out the history of the villain and the purpose of his actions.

It's pretty easy to see that you can use any of these methods to infinitely extend a story. More importantly, it can be used to add interest to a story. If you were reading a story where the character says, "Now that I know where he is, I'm going to hunt him down and kill him", and the very next line is a piece of narration that says, "He arrived at the castle." It glosses over a great amount of time that passed in the story's world, which could have been spent developing the character or having him jump through hoops so that we start rooting for and caring about him.

The other reason to do these quest modifications is that they add excitement to the story. You can tell any story in a sentence (in the example I've been making up, it is "the hero gets wronged and kills the person who did it"). But stories are more than one sentence. So when you tell your story in more than one sentence, make it more interesting than a one sentence story. Now you have a few ways to do so.