I have to have my gum. I chew two or three pieces a day. It's just one of those little habits: I chew. If I don't have a piece of gum, I chew my tongue or the inside of my cheek. If I'm bending over something looking intrigued and you hear a muted squishy noise, that's probably me chomping down on my tongue. No wonder I'm starting to eat spicy food these days; I'm probably dulling my nerves.
It's a silly, random thing. A tiny detail. But everyone has a little detail like that, a quirk that makes them unique.
That's the stuff you have to pick up on when you're writing a story. People aren't just walking, talking, emoting, reacting machines. They don't just cry at sad stuff and punch the bad guy when it's time for a fight scene. They also worry about food between their teeth at meetings. They refuse to wear sunglasses because it feels claustrophobic. They chew their tongue.
People think that every detail has to be connected to the plot. But the problem is, none of us is ever made up of one story at a time. There may be something big going on in your life, but the tiny stories we live out--about flossing our teeth obsessively out of fear of floating broccoli--are also going on all the time. To make a person real, you have to include these details. Just here and there. Just a little. It's those things that make readers feel like we know someone--like we can know them.
Another thing about characters is that their back-stories aren't usually spectacular. Few people had a giant explosion of action in their past that caused today's plot to take place. It's the little things building on each other like a pile of stones that make life's markers.
I'm a vocalist. I've been singing my whole life. My family is very musical. I sang in choirs growing up and then in church and then later in fun band projects with friends. I was never in a real band. I've never had professional singing lessons. I'm not about to abandon my current career and become a professional singer. I didn't have some blinding flash of light in my childhood where an angel told me I should sing. I just sing.
Singing is a part of my life, but there's not real explanation for it. There's no big instigating event. No long-term build up, no years of training and yearning and dreaming. Just doing it on the side, never really thinking about it, never letting it take a front seat in my life. Yet it's a part of who I am.
People are like that. You don't have to have some all-encompassing explanation for why your character decided to become a cop/pirate/dragon-keeper or why they're out for revenge/afraid of people/the lone wolf. There's rarely a simple reason why people in real life do these things,* so the answer shouldn't be easy in a book, either. I think we're a little tired of the parents-got-murdered version of shaping a character's destiny. Why can't they just be stubborn as a personality type? What about a character who doesn't know why he became a pirate? That's way more interesting. And it makes the climax of the book all the more climactic: this is the first spectacular event in his/her life.
In order to write realistic characters, you have to observe first, then imagine. Observe what real people do. Observe the little stuff. You don't even have to know the person. Just watch what they do; the way she keeps tucking her hair behind her ear, or the way he lights up a cigarette whenever he's nervous only to put it out a few seconds later.
Then imagine it in a slightly different scenario. Instead of an ear-tucker or a cigarette-lighter, how about a character who tucks a cigarette behind their ear whenever they leave the house, as a sort of paranoid precaution? Imagine a hundred different scenarios; run them through your head and observe them like you observed the people. Does it look real or stiff? I know something's wrong in my plot when I let it play out as a mental movie and the acting looks flat.
What are your foibles? The quirks of your friends that make you laugh? The oddities of your family members that drive you up one wall and down the other? Those are the things that will flesh out your character. And don't come up with a reason why they're like that; Alfred doesn't have to be a schizophrenic ex-soldier with PTSD in order to have a tick. It's amazing what just a few sentences, a trivial thematic thread, can do to make someone come alive.
Ps. You have my permission to write about a tongue-biter. I would feel honored.
Word count: 871.
* If you know someone who keeps dragons in real life, please introduce me!