Your story needs a hero. Unless the book you’re writing is a depiction of darkness where you suck your readers in then offer them nothing but despair, in which case, fair enough, the monsters win.
While villains often get the credit for being the more interesting characters, the Banes, Jokers and Darth Vaders of the world, the protagonists and the heroes of our stories are what keep the narrative moving. The villains create a problem, and the decisions of your hero impact how the story progresses through that problem. Their action and inaction are the twists and turns in your plot.
Your hero needs to have the ability to act. Readers rely on the hero solve problems and in order to do that your hero needs decisiveness. This will not only help your readers trust in the hero, but it will also keep the pace of your story from stagnating.
Your hero should have something to lose. Their decisions should have a consequence beyond just the greater good. The vast majority of your readers won’t be able to relate to saving the world, but they’ll be able to relate to the fear of losing a loved one or losing the trust of a companion.
People change and so should your hero. Throughout the course of your narrative your hero should be tried and tested and put into dangerous situations that may call on them to make difficult decisions. Think about how these situations would change you. Maybe your hero becomes darker, maybe they adapt or maybe it breaks them. Change will keep your readers interested. You don’t want to become predictable.
Your hero needs a secret. This can be a secret from other characters. The revelation of this secret could be the destruction of your hero and the reader will be kept in agonizing suspense as other characters get closer to learning the secret. Or, the secret could be kept from the readers. What hidden truth is your hero hiding, if done well by the end of your story the readers will be dying to know what it is.
Most importantly your hero should be relatable, someone a reader, no matter their background, can understand and connect with. Superman may be a god-like hero, but he still struggles with human issues, morality, love, trust. If your hero is without flaw and flies through your book slaying bad guys and wooing their love without hassle then your reader will become bored. Maybe your hero can fight off 50 enemies at once but stumbles over words around a beautiful stranger. Or maybe they can charm a whole room of people, but cower at any sign of violence. A perfect hero should be an imperfect person, driven by an everyday want, hope, or fear.
“What's unique about your hero and what makes your reader fall in love with your hero is their particular perspective, your hero's rose-tinted glasses. How does your hero's thoughts, feelings, and actions impact how they view their surroundings?” -
Sacha Black, talking to Joanna Penn. Definitely check out their whole conversation here.