The first time I wrote a realistic character I thought:
Where did that come from?
So I set about trying to understand my characters. As it turns out, characters need very little prodding to come into existence, and the best writers will often find themselves holding tightly to the leash while their character tries to sprint.
To plan for a character is easy. A character is simply an intersection of the following information:
A past
A temperament
A social structure (or a lack of one)
A set of goals and fears
Once you map out these data points, you can begin writing about your character, putting him/her/they in situations and settings to see how they react. What you will find is the information above will lead you to write your character’s actions in a particular way.
For example:
Imagine you are beginning your story with one character. You set out to build this character by using the above character profile.
Past: Character is a teen girl who lives with her father. Her mother has abandoned them, and has run off never to be seen again.
Temperament: From her father, the girl has learned poise and consistency, but from her mother she has gained an overly altruistic sensibility, seeing every personal relationship as a chance to be hurt and abandoned again.
Social Structure: The girl is part of a close friend group at her school. She has known her friends since a very early age. The group has reached an age of sexual maturity, and are beginning to, for the first time, see one another as possible romantic partners.
Goals and Fears: The girl would like to go to college and eventually run her father’s company. Along the way though, she would like to gain a full college experience and have a ton of fun. Eventually she would like to be married and have children, though it isn’t her primary goal. She is deathly afraid of abandonment, which will impact all of her future relationships.
This character profile gives you a place to begin. Many new fiction writers fall into the trap of worrying too much about the characters physical appearance, because they want the reader to be able to picture him/her/they in their heads. Imagery does not form a plot though. I have found that it’s more effective to focus on the above character traits, and to give liberties to the reader on the character’s appearance, while dropping small, sporadic hints toward the character’s image.
After you’ve created profiles on your characters, it’s time to get to know them. The best way I’ve found to do this is to drop them in situations (scenes) to see what they do. This is where the unconscious part of fiction writing comes in. You will find that if you have enough of an idea who your characters are, you will unconsciously begin to have them interact with one another as if they are doing so autonomously.
Character-relations become especially strong when their goals and fears begin to collide and interact.
From data points of individual characters arise a plot and a tone. Once you have built your world and the characters within it, you begin to chart out a point to the story as they interact with one another within the world. Their interactions create conflict, and conflict drives narrative. When a conflict arises, you will sense that this character should begin to look for a solution, and their solutions will often create conflict within another character's profile of data points. This interplay continues throughout your story, using cause and effect, until you find a resolution point. This will mark the end of your story.
Note: You do not need to create all of your characters at the beginning. It is far easier to begin with just two, and to add extra as needed as your conflicts and resolutions bloat and retract.