Readers, myself included don’t like cookie cutter, cardboard cutouts as characters. If a character is boring or not dysfunctional enough, I’m putting the book down.
As a writer I learned that the more layers a character has, the better your audience receives the character. That character’s bio doesn’t have to be explained in detail in the book, but it may be something you want to keep in the back of you head as you’re writing.
What’s their favorite food? What are their hobbies? What was their relationship with their parents? Do they have tattoos? Did they serve in the military? What type of movies do they like? Who’s their best friend? Where did they grow up? Do they have money? If so how much?
The answers to all those questions and everything else you can dream up for your character will influence every challenge they have to face, just like what you faced in the past affects who you are today.
For example, our main character in The Body Hunters, Danielle Labouleaux or Danny as she prefers to be called is biracial and grew up in New Orleans where she had a somewhat antagonistic relationship with her parents in her teens and early twenties. She was bullied as a child, not only for being biracial and also for a zipper scar that bisects her chest from heart surgery when she was six. She has a penchant for hot rods, especially her candy apple red Camaro, named Lucille. She loves to cook, which she learned from her Grandmere and she hangs on to friends for dear life because they were few and far between during her childhood. She also has a thing for buff, tattooed bad boys, who are really diamonds in the rough.
This is how we started our main characters and as Danielle’s story progressed, we added layers and layers of back story, fleshing her out as a character. Before long we knew what she’d say and how she’d react in any given situation.
The same technique can be used for the universe your characters exist in. It’s your universe, you make it up and mold it any way you want to.
Is it post apocalyptic? If so how did it get that way? Who’s the President? Is this the future? What happened twenty years ago?
The more believable your story and character are, the more invested your readers become in your story.