For the record, "Protagonist" = good guy, "Antagonist" = bad guy.
Pick one of them. It doesn't matter which, because eventually you're going to do this for all of them - every character, no matter how small.
As in life, everyone in your story is somehow different from everyone else. For example, I am an introvert who loves thunderstorms and Starbucks Cinnamon Dolce Latte. I enjoy chatting with interesting people, but have a lousy memory for just about everything. Let's say I have a friend (This is an imaginary friend. Nobody get defensive!) who has a quick temper, loves fried food, hates time wasters, but can sit for hours petting her cat for comfort.
Let's say she calls, wants me to go in for coffee and talk about business.
"Motivation" is the reason she and I will or will not go.
She is motivated because she likes to keep busy and on top of all things efficient. She knows I like my Starbucks latte, so is using that to lure me, knowing it usually takes a crowbar to pry me off my keyboard. Her hidden motivation is to ask me to join a committee because she is overwhelmed by all the hours it's requiring of her.
I am motivated because I haven't had a latte in a week and my social life is ebbing. But I have a deadline for my latest editing job and use that as an excuse. I apologize and take a rain check.
Would your protagonist go with her? Why or why not?
How do you know the answer to those questions? Because you know your characters inside and out. They are not cardboard cut-outs, or at least they shouldn't be. They need to be real. My all-time favourite mentor, Rona Altrows, taught me this lesson in one easy phrase. Ironically enough, she suggested I take my characters out for coffee. Once there, I would get to know that character as I would anyone in "real life". How do you do that? Ask questions. And don't just whip off the answers. Sit down and plan on a good, quality interview. Get into that character's head, help the reader . Here are a few questions to get you started.
- Do you like loud parties ... and why?
- Who is your favourite author ... and why?
- What is your favourite kind of music ... and why?
- Who is your best friend ... and why?
- Are you close to your family?
- Do you like to drive or be a passenger?
- Do you shop with credit cards or cash?
- Do you have a debt?
- What's your bedroom like?
- Are you, or have you ever been, in love?
- Are you more of a cat person or a dog person?
- What's your favourite meal, and do you like to cook?
From the answers, you can see into that person. Deduce if they are an introvert or extrovert, if they like to live on the edge or push boundaries, do they "work to live or live to work", if they are the kind of person who would enjoy a coffee with that kind of friend.
You don't have to hit us over the head with character information. Be subtle. Say your character owes some pretty big money. No need to remind us repeatedly of that. Just slip in the occasional hint, like when she sips on her latte she admits she shouldn't be spending her money on frivolities like a latte. But why did she go then? Did she think her friend could help with her money difficulties perhaps? And what if her friend refuses? What if her friend is offended and stomps off, ready to announce your character's woes to the world? After all, that could be in the other character's personality.
Once you know your character(s) well enough, you can determine his/her reasons for what they do in the book. You know what path they will naturally follow. HOWEVER, you will also know how far you can push them before they snap and do something "out of character". As much as a character is interesting on his/her own, the moment when they jump the opposite way can be pivotal to the story.
Character Motivation, or lack thereof, can make or break a story . Make it believable that certain characters would or would not do certain things. And help the reader care about that character. Make him/her deep enough that we understand them and we say "Yes! That's what he would do there!" or "I can't believe he did that, but it might just work ..."