Character building starts from the inside out. You don’t start with a tall, slim 18-year old girl who is good in math and popular in school. (Don’t you hate her already?)
You start with the characteristics that will work best in this story. What do you need? The main character will drive the story. His or her decisions will create the conflict and interest.
Yes, things will have happened to her – she may have been abused, bullied, picked on, chosen for Prom Queen. But it’s what she does about it that creates the story. It’s what she has had to deal with – negative or positive – and how she has reacted that guides the story.
She will deal with her life in the way that seems best to her at the time – just as we all do. She will base her reactions on her values and on her past experience. If she truly values loyalty she will not let her best friend down.
You can push her to the limit and she will not let the friend down. But perhaps she values honesty more than loyalty. When she is pressed she will not lie for her friend. The story twists.
It can seem reasonable to create characters with values like your own. After all, they’re pretty good, right? It seems reasonable to value safety and security but if that person values security so highly that they amass money and consider it more important than people, friendships, honesty etc. then you’ve got an antagonist in the making.
And he isn’t truly a bad person, he’s just very insecure and he’s gone overboard on security building. In your story, if you press him he will choose money. He will let down a friend in an emergency. The story might turn on this.
To go back to our 18-year old. How did she become popular? What do classmates say about her when she isn’t there? How does she feel about her looks? Was she driven to succeed in school?
Figuring out the answers to these questions builds a character who is believable and with whom readers will empathize. Even if she is the one who is insecure and grasping for money and resources her friends (and your readers) will go along with her.
You’ve given your character a good strong base to take on the challenges that lie ahead. You have a character that has an internal life and is not just a stereotype. By now you are starting to feel this person and not just think them.
Your readers will feel them too and be drawn into the story.