Whether you're a Seat-of-your-pants writer, a perfectionist at plotting, or a healthy mix of both, the one thing you need to keep in mind with your story is its structure.
Structurally speaking, stories follow a pattern. And as humans who've been telling and enjoying stories for centuries we've come to understand innately the pattern that a story goes through before it reaches its end. The Story doesn't feel whole when one of the components is missing.
In the most rudimentary terms, something needs to happen. Otherwise we're not moving people down a story-line with an ending. We don't want to simply describe something (although they can be compelling and beautifully written). It's simply not a story.
Basically stated, the story needs to have a beginning, a middle, and an end. Three parts that take the reader or listener on a journey, just like we learned from the movie "The Prestige" that magic tricks have three parts as well: the pledge, the turn, and the prestige.
We're going to dive a little deeper into these sections and break them down further, but first, let's describe them just so we're on the same page.
In the beginning, we present a person or object in stasis. We offer their particular set of normal circumstances, so the reader understands where the character is coming from and can relate.
Quickly, we bring in the "But then" moment where the stasis is upturned. The subject must deal or plan around this new event and the journey back to normality begins. (Or if we'd like to keep with the magic terms, this is the Pledge.)
The Beginning includes:
-The Hook - a well written first sentence that starts the story off in an interesting, compelling way that arrests the reader's attention.
-A brief(ish) description of life before the event that sets our subject on this new course of action.
-Small preliminary struggles (doubts, etc) that convince the hero that they need to begin their journey.
The middle is where the subject struggles against amassing objections to their stasis. These struggles pile higher, making the subject try harder and use more energy to solve problems.
Eventually, the critical point is in sight and must be overcome. There is no other alternative for the subject and the suspense runs high. (This is the Turn.)
The Middle includes:
-A few twists and turns, fraught with peril, where the hero will be tested and grow from least troubling issue to most troubling issue.
-A few wins and growing pains for the hero.
(We'll discuss this more in depth in a moment.)
Then in the end, the hero must conquer the villain. The stasis must be achieved, but not the original stasis. Our subject has been changed by the story. So, they must come to terms with a new stasis that is equally or more satisfying than the first. (This is the Prestige.)
The End includes:
-The ending battle or Climax
-An ending sentence that wraps up the story with a neat little bow.
These are the basic parts of the story that it needs to feel complete,
Now, like I said previously, the middle has a little bit more to it, and different authors have different ways of structuring their stories. So, here are a few other authors suggestions.
Steven Pressfield talks about the Hero's Journey in his book "Nobody Wants to Read your S***" and how it folds into the Three-Act structure he learned writing screenplays in Hollywood.
It goes like this:
1. Hero starts in Ordinary World.
2. Hero receives Call to Adventure.
3. Hero rejects Call.
4. Hero meets Mentor. Mentor gives hero courage to accept Call.
5. Hero crosses Threshold, enters Special World.
6. Hero encounters enemies and allies, undergoes ordeal that will serve as his Initiation.
7. Hero confronts Villain, acquires Treasure.
8. The Road Back. Hero escapes Special World, trying to "get home."
9. Villain pursues Hero. Hero must fight/escape again.
10. Hero returns home with Treasure, reintegrates into Ordinary World but now as a changed person, thanks to his ordeal and experiences on his journey.
(There's more detail in the book. I'd recommend checking it out.)
Putting together the Hero's Journey with the Three-Act Structure gives you a story.
Author Joe Nassise did a Webinar with Nick Stephenson explaining how he plots out his stories and finishes writing his books in 30 days.
He breaks story writing into 4 Phases.
Preparation Phase (Beginning)
Reactive Phase (Middle)
Proactive Phase (Middle)
Conclusion Phase (End)
And he identifies 3 Game Changing Events that bind the phases together and transitions between them. So, while his characters journey, he has a purpose behind each phase they enter and a scene that moves them smoothly into the next phase.
As you can see in the examples above, the general rule is that your middle should have some substance where in the stakes go up and the adventure gets treacherous.
Overall, listen to your story. You can tell what's working and not working based on how it feels to you as a reader.