Your story is done―or maybe you're just done with it. Now what? Now you rewrite the ending.
More than any other aspect of the story, the ending is what your reader will most remember.
Listen to people talk about movies. What's the reason they give for not wasting your money? "It was okay, but I hated the ending." People don't usually like movies except for the characters, or the setting, or the progression to the second plot point. When people complain, it's usually about the final fifteen minutes.
When you rewrite your ending, what you're trying for is an ending that seems natural, even if surprising. Whether tragic or happy, the ending should seem inevitable. How that ending is reached is where you tweak expectations.
There are a few structures that help create that impression.
The ending can circle back to the beginning. If the story starts with the main character sitting alone in a coffee shop, end the story with a similar scene.
The circular ending can imply either a return to normalcy or stagnation, depending on mood and genre of the story.
The ending can provide counterpoint to the beginning. If the story starts with the main character sitting alone in a coffee shop, end the story with the character surrounded by friends and family.
The counterpoint ending can imply change, for better or for worse, depending on the story.
Both structures give the reader the subconscious impression that you knew what you were doing when you wrote the story. You didn't just tack on an ending. You didn't just stop because you didn't know what to write next, or because dinner was ready. You controlled the material.
Yet another way that you need to shape the ending is by deciding where to place THE END.
Generally speaking, you want to get out as soon as possible. Depending on the story, however, that point in the narrative shifts.
Let's say the story started with the main character accepting a quest. As soon as the character finishes the quest, you could finish the story.
But what if you want to show that the journey is more important to the character than the destination? You move the ending out. The character finishes the quest, and then returns to square one or experiences a transformation. The character, however, soon feels unfulfilled and searches for the next adventure.
Or maybe the quest was simply a way to challenge the character in order to promote growth, and the real reward coming afterwards, with the consummation of an earned relationship.
Which provides yet another way to place THE END.
Once the consummation is inevitable, you can stop without reaching it. The reader then projects the rest of the story after reaching THE END.
If there are several sub-plots, tie them up before reaching the conclusion of the main plot. (Romance sometimes being the exception.)
If there are both internal and external challenges for the main character, try to keep the resolutions as close as possible, and intertwined if you can.
Overcoming guilt, the character is freed to act. Or, the character acts, thereby putting feelings of guilt to rest.
Are there several themes you touch on throughout the story? Try to echo them in your ending.
What type of story are you writing? What kind of ending does the reader expect? How far can you stray from the conventions, if at all?
Ask other people to read the story cold. Are they satisfied by the ending? Did they understand all the things you thought obvious?
If so, stop.