One of the things I’ve struggled with a lot in the past, especially in the context of my own universe, is knowing what is and is not important for the reader to know. Specifically, I’m referring to the ‘scenes’ the author shows. Pretty much zero books will encapsulate every moment in a character’s life, even if the chapters are continuous. For example, how often does any character in any fiction book you’ve ever read eat? How often do they use the restroom? How well do they sleep at night?
These are examples of something a reader doesn’t need. Unless your story is about a person trying to survive, taking an extra effort to establish that your characters are eating regularly is unnecessary. “Hold on,” you may ask. “Does this mean putting food in a story is pointless?”
Certainly not. Food is still important for your characters. It is simply going to be in the background the whole time. If your characters are having a feast, that ‘scene’ is not going to be about the food they’re eating, but the character interactions therein, or the information somebody receives. It is a nice detail to add what food they are eating, but it is never the focal point of the story.
Consider Lord of the Rings here. Very few times during their journey does Tolkien describe to us a meal that they have. We can assume that they are eating, so in order to establish to the reader what is going on, we can simply say “Before they departed from the land of Lothlorien, the elves give the fellowship waybread.” After describing what this bread does and how much of it the party has, we can rest assured that food is not going to be relevant to the reader unless the author decides otherwise. We only need to know what a character is eating if it is a concern for the character, too.
The general rule here is that everything is assumed to be fine unless the author tells the reader it isn’t. We always assume a character is well until the author tells us he is sick (though conveniently making the protagonist catch a cold just to make the next scenes harder for them could annoy some readers, even if it is a possibility in the real world). So basic physiological necessities are never a concern for a reader. They’re focused on the story, after all. They don’t need to read about your characters taking potty breaks.
But the more prevalent question here is worldbuilding. This applies more to sci-fi and fantasy writers than anyone else. New writers are notorious for the dreaded “info dump”: pages and pages of explanations of a nation or character’s background with no actual scene happening. Tolkien is a great example of this here, too. An editor in today’s market would have thrown out Fellowship of the Ring because the forty page prologue has no setting: it’s all set-up.
Funny enough, as much of a problem as it seems to be, it’s an easy fix: just take it out. If you have to explain something to the reader, just don’t. If I already know everything about a character’s history and past experience, I won’t care to see how they interact with others in the story. But if the first impression I’m making of this character is through dialogue, I’m going to have to guess what this character’s history and past experience is. And here’s the thing.
It’s okay for the reader to guess wrong.
The best authors in today’s world force readers to guess and predict. Patrick Rothfuss’ Kingkiller Chronicle is a trilogy describing the life of Kvothe, a man with many names spoken of in legend and whispers. The third book isn’t out yet, and we the readers still have no idea why he has the title ‘Kingkiller’. There is implication there, obviously, but in the end, we just don’t know. This is why books like this do so well. They force the reader to ask huge questions that we don’t get answers to until much later on.
So if you’re building your own sci-fi or fantasy world, complete with nations and politics, and you don’t know the answer to the question “How much do I tell the reader?” The answer is probably going to be ‘very little’. The Archive of Nacre Then is over seventy pages long. I’d say over eighty percent of it has never been mentioned or even hinted in any of the fiction I’ve ever written in the universe. The reader doesn’t care about a desert bird that pecks rocks to find turtles, so if it’s never important to a story, it should never be mentioned. Does that mean those birds shouldn’t exist? Of course not! It helps me as the author develop a complete and dynamic world. Elements like this that the reader will never see are still crucial because these birds will at least indirectly influence the culture of people around them, and the more pieces that I have, the larger this world will be.
Think of a fictional universe like an iceberg. Ninety percent of an iceberg is submerged. Somebody looking at this iceberg will never see that ninety percent. But the larger the iceberg gets, the larger that ten percent is, and the more detailed this universe seems to the observer.