This particular post is dedicated almost entirely to Fiction. Non-fiction has the same elements, but they're almost always going to be done in a Character based structure. So while it will be helpful to know the other three structures, it's not entirely essential.
The MICE Quotient is something every author instinctively knows but has never actively thought about until it was presented to them point-blank. It's not always introduced as "the MICE Quotient," but it's the way I learned, and it's the way that makes the most sense to me. The term itself was coined by Orson Scott Card and the 'official' breakdown is found in his book Character and Viewpoint (link available in the Links section). The very basic premise of the MICE Quotient is thus:
These are the four basic narrative structures every story has. Each structure is necessary to the whole story, you can't make an Idea work without Character or have an Event without a Milieu, but there is always going to be one element that stands out a little more prominently in the Narrative. For example, The Hobbit would be considered a Milieu story because the structure follows (very basically) the "There and Back Again" method. It's even in the subtitle (or the runic translation depending on which version you have).
So this is how the structures break down:
Milieu: There is a new world (whether literally or simply according to your character's perception) which needs to be explored. In general, this type of structure follows the 'there and back again' model where the Character leaves their comfortable life (either by choice or by force) and ventures out into the unknown. They always encounter new, unusual, and often fantastical things before eventually returning home a changed person. Well known stories that follow this Structure are, as previously stated, The Hobbit as well as The Tale of Gulliver's Travels, the film Avatar, and The Lion, the Witch and the Wardrobe. This structure is most popular in the Fantasy and Science Fiction genres as it allows the author to show off the world (or worlds) they spent hours, days, weeks, and sometimes years perfecting.
Idea: There is a question that needs an answer. Someone has died mysteriously, an object has disappeared, a well-established person in a community is acting strangely, etc. The point of the idea structure is to answer that question. When a story opens with a "Why" it logically follows that the story ends when the "Why" is answered. Why is this person dead? Because they were embezzling money from the Mob (which also explains who killed him). Why has this object disappeared? Because it had magical properties that the Vizier wanted (which also explains who took it). Why is this person acting strangely? Because they're suddenly being blackmailed for something that happened twenty years ago. This structure is, obviously, used the most often in the Mystery and Horror genres because it adds suspense and gets the reader guessing.
Character: There is a shift in a Person's life. It could be a small shift such as a move to a new area or it could be a large shift like surviving a natural disaster, but this structure is based entirely around the life and perceptions of a single Character. Other characters will naturally be a factor, your Character doesn't live in a vacuum after all, but if the story starts with the shift of a single Character's life, it doesn't end until that shift is justified and settled. That could mean that your Character manages to make a successful move from their old life into a new life, that they fail and return to their old life, that they fail and find another new life, or that they fail and die. Well-known Character stories include Twilight (the first book in particular), The Hunger Games (again, first book), Pride and Prejudice, and Ender's Game. This structure is commonly used in Coming of Age stories as it follows a very specific character arch.
Event: There is something wrong with the world that needs to be fixed. This could be a political element, a natural disaster, epidemic, evil empire, etc. The options for this genre are fairly limitless. The point of the Event story is that something Epic is about to change everything (or already has changed everything) and needs to be prevented, reversed, or changed. The movie Deep Impact uses the event structure by introducing a giant asteroid that is going to crash into the Earth, and then it proceeds to show the reactions to that Event. Astronauts try to destroy the asteroid, the governments build Impact Bunkers, citizens panic and riot in the street, but in the end, the disaster is averted and the people go back to living their normal lives. That's the basis: something happens, people react, and that 'something' unhappens somehow. Popular stories which follow this structure are The Lord of the Rings, the original Star Wars trilogy, War of the Worlds, and Eragon. Again, this structure is often used in Science Fiction and Fantasy, especially in previously established worlds.
As I said before, all of these structures are present in every narrative (prose, plays, and movies) but some are more downplayed while others are more prominent. The best thing to do with your story is to figure out which is the most important to you. Is it a Fantastical World, a Burning Question, an Intriguing Character, or a Cataclysmic Event? Figure it out and then write to your tastes, there are always readers for what you write so long as you write it well, so you might as well enjoy what you're writing ^-^