An average book has average expectations, and that means a reader doesn't want to spend extra time reading it or figuring it out. That is where those genre length expectations come from. If the reader just "liked it" she will be more likely to notice if it was too short or too long.
Though every book has its detractors, I want to use two examples of books at opposite ends of the length spectrum. Very few people who love Diana Gabaldon's Outlander book would suggest it is too long. It is a very long book at 850+ pages. But the reader immediately comes to care for Jamie and Claire and sticks with it because she wants to be sure they are okay in the end. Many readers report reading the entire book in three days because it moved so quickly. Hard to imagine an 850 page book moving quickly.
On the other side of the spectrum, few would suggest that 1982 National Book Award winner, William Maxwell's , one hundred thirty five page book, So Long, See You Tomorrow is too short. One reviewer wrote what I believe is true of this story: "...it can seem at times that whole paragraphs of unwritten backstory are suggested by every line, every image." Though it is novella length, those who love this spare book can't forget it. It "felt" like a longer book because of how well-written it is.
Could Outlander have been written in under 300 pages if the author had only been more spare with her words? No, it couldn't because it was of epic scope--covering history, time travel, and a grand quest. It worked because of the characters AND because of the universal themes of honor, betrayal, vengeance, love, and forgiveness. Should So Long, See You Tomorrow have been expanded to 250 pages or more? No. Though the themes are also universal--coming of age, innocence betrayed, grief, guilt, loss--the story setting is small town in the 1920's. In other words, both books are the proper length for the story. Neither book has let down it's readers because the underlying craft is superior and that trumps length every time.
Though most of us will not write a bestseller or win a book award, we should still pay attention to good craft. It is that craft that keeps a reader engaged and negates length expectations. It is also important to know that storytelling expectations change from generation to generation and certainly from one century to the next. The classics you may have read in English class, written in the 19th or early to mid 20th century, does not meet modern story telling expectations today. For the most part readers expect to be constantly driven forward from the first page to the last, with the promise of the first pages being delivered in the end. Also character, particularly in genre fiction, is the primary driving force. It used to be that setting or theme was enough. Not anymore. When competing with television and movies that can display visual setting and deliver theme through musical pathos, it is only character that stands apart.
How does the writer meet story expectations?
Depending on which craft book you read or storyteller advice you follow, the elements can range from the three most important to hundreds of interweaving elements and structures that can make the story better. In the interest of brevity, I am not going to reiterate all the typical things you can read in any good craft book (setting, plot, climax, structure, etc.). All those are important. I will assume you've already done all that to the best of your ability. Instead, I've chosen what I believe are the big storytelling expectations of readers. The six big things often conflate setting, plot, structure, and character together in service of the story expectations. I believe these six items are what make a reader forgive small mistakes, suspend disbelief, and in the end recommend your book to others.
- Have something to say (often known as the central premise or primary theme). The more that your book can relate to a theme/message that is larger or more universal than the story you are telling, the more most readers will like it. In other words, though your story may be about one individual unraveling a mystery in a small town, it needs to be more. Is it about the corruption of power? That love conquers all? That good and evil are the same? My themes tend to be similar and interrelated no matter what I write. They are: "Everyone is wounded and can only find their true path by overcoming their past;" and "We all have good and evil inside us; life is about constantly choosing which to favor."
Can you articulate your central premise in a single line? If not, that's a problem. It means you either don't know it or don't have one. Knowing your primary theme will help you look at every action your characters take, every setting you have them in, and the arc that needs to occur for the characters and the story. Every element of your story should have some echo of this central premise.
- Ambition through character development. All craft books talk about character arc and development--the need for three-dimensional characters, to articulate the character's goal, motivation, and conflict (GMC). All of this is true and important. Beyond that, though, the character reinforcement in the reader's mind is directly related to the writer's "ambition" in character development.
Great books connect the theme/central premise to the reader through one or more characters. Those characters provide an example of something the reader can use in her own life and how to get there. It is never easy, and the reader may not know until the end that it's happening, but it leaves the reader satisfied. A reader will forgive a number of faults, suspension of disbelief errors, if she identifies with your character(s) and can use what she learns in her own life--not in a literal way, but in a metaphorical way. For example, why do readers love paranormal books? It's not because they believe they can solve problems by fighting a literal dragon. It is because the character must overcome the fear of fighting the dragon, of not being good enough, of perhaps not being allowed to fight, or many other obstacles that a reader can relate to her own life. That is what "ambition through character development" creates--a direct connection to the reader's life, no matter where the story takes place.
- A single over-riding through line (character motivation). When I beta read a book for new writers and provide a critique, the most common mistake I see is a fractured storyline.
That is where there are too many bits, or scenes, that do not move the story forward, do not solve the primary question. Instead writer's go off on tangents with two many other characters, settings, backstory, and in the process the reader also loses her motivation to continue reading. This is not to say your plot or characters need to be simple. However, if you are not always marching forward and reminding the reader that your character will get what he/she wants, you are not meeting expectations.
The concept of a through line was first used by method acting teacher, Stanislavski, as a way for actors to better understand their characters. He believed that actors needed to go beyond what the character was thinking or doing in any particular scene. In order to fully embody the character, an actor needed to understand the "through line"--that which pushed the character forward and thus linked everything the character did. Even if your character is having a cup of coffee in a scene, the reader wants to know that having this cup of coffee with this particular person, at this particular moment, is critical to that character getting what he/she wants in the end. If it is not important to that motivation, the scene should not be there.
- Nothing comes easy (character torture and change). Another area where reader expectations are not met by the story is when everything happens miraculously. In other words, the character never has to fight for what she wants. Good stories not only show the character changing from beginning to end, but they also make it torturous for the character to change. This also goes back to ambition. If your protagonist is an alcoholic and your through line is overcoming wounds of the past, then she needs to end the story being sober. More than that the journey to sobriety needs to be fraught with pain--moving forward, sliding backward--and times when the reader will wonder if she can really pull it off.
Taking the alcoholic example again, too often a character will act the alcoholic until the climax when a single event miraculously turns her around (meets the guy who accepts her, reconciles with her mother, almost dies in a car accident). Though these events may be ways in which someone changes, it doesn't meet the "ambition" requirement. A reader cannot easily identify with a sudden miracle. (Even in Inspirational fiction the character still has to work at believing, at making life move forward without miraculous intervention) A reader can identify with the character working at it throughout the book, having problems, backsliding, moving forward, getting closer and closer and then the "miraculous, life-changing event" caps it. But without all that lead up and trying and getting closer, the reader says "Meh. Unfair. Not satisfied."
- A page turner (some call this pacing and tension). You often hear a satisfied reader say something like: "I just kept turning the pages. I couldn't put it down." Authors often mistake this need to create a page-turner with external conflict. They create tension by starting a fire, throwing in a bomb, killing off a character, shooting somebody, giving her amnesia--in other words making something big and horrible happen. Though that is a technique, when it is overused it becomes silly and obvious to the reader because the fire, bomb, killing, etc. has nothing to do with the central premise and the reader feels manipulated instead of satisfied.
Readers will turn the page if you are driving the through line. Readers will turn the page if they care about what happens to your character. Readers will turn the page if they are invested emotionally in the final outcome. Just as in a great mystery, a good writer lays clues and red herrings, works in both internal and external tension, may even find the solution at the climax only to learn they were wrong, there is more work to be done until the end. This is a good recipe for all other fiction. Whether a romance, science fiction, a fantasy, or a thriller it moves in a similar fashion. There are clues as to whether the character(s) are moving toward their goals or not; there are times the reader believes everything is fine when it's not; there are times the reader believes the character will never make it but the character still does not give up; and so the reader does not give up.
- Deliver on your promise. The opening of each book makes a promise. It sets up expectations--partly based on the genre the reader believes she is encountering and partly based on what happened in your opening hook. Anytime you move away from that promise, the reader becomes insecure. Sometimes that is good, most of the time it is a chance for the reader to put down the book. Most important, when the reader closes the book, she will be satisfied if you deliver on that promise.
For example, if you open with a big event (like a bomb in the middle of town that destroys your heroines family) then the reader is going to expect that book to be equally exciting throughout and that your heroine is going to suffer from that event. If you did that just to have a hook but it had nothing to do with your story, your reader will crucify you in reviews. You don't have to open big, but you have to start where change is occurring. Then make sure you realize what the promise is that you are making--what will you have to deliver throughout the book.
One of my favorite SF authors is Octavia Butler. Every opening of her novels meets both the genre promise and the novel promise. Every ending delivers on that promise. For example, in Dawn, the first book in her Xenogenesis trilogy, it opens like this:
Alive . . . again.
Even if I didn't know the author, I would immediately be drawn in. What is happening? Did she die three times? Is this about death? time? confinement? control? Within the first few pages, the reader learns the human protagonist is a captive and in a strange, alien environment that questions time, death and life, and control. That means the reader now expects that one or more of three things will happen: 1) the protagonist will find a way to escape her captivity and punish the captors; 2) the protagonist will find a way to make a life within captivity; and/or 3) the story will define what it is to be human and how one chooses to retain or give up one's humanity. If none of those promises is delivered, the reader will be lost and feel dissatisfied. If anywhere along the way the heroine is not either trying to escape captivity or learning to live a fulfilled life within it, then the reader is dissatisfied.
Check out one or more of your favorite books. Read the first paragraph and ask, what is being promised? Was it delivered? Read the first five pages and ask the same thing?