One of the best questions you can ask of your story-in-development is: Why is this character in this story? That is, why this character and not some other? What is it about this story problem that will hook the major character (MC) and shake them to their core?
I am, of course, talking about desire and its corollary, fear. The MC should be a little larger than life. Not passive and coasting along, but caught (or soon to be caught by the plot events) in the grip of a deep desire and a believable fear (of failure.)
The homely plot.
Thing is, sometimes we forget how powerful it is when the desire and fear are specifically and deeply related to the plot. When those airy, subtle and complex character traits that we have worked out have their feet deep in the muck. The muck of your plot.
For example, Cinderella’s deep-seated desire for love is knit into a plot about a royal ball from which she is socially and financially excluded. In the Temeraire novel, Victory of Eagles, a captain in Her Majesty’s military service, who loves honor above all else, is ordered to take a dishonorable action.
It is not a requirement to knit your plot with a very deep desire. Book one of The Hunger Games is an example of a MC whose inner nature is not much played upon by the plot. (I’m not saying the characterization is weak. Just that it’s not tied to the plot problem.) Sometimes you get hold of an idea that is so strong that to add another layer is beside the point. But it’s risky to count on it. I usually strive to make the plot impinge on a characters defining desire beyond the will to live. I.e., the protagonist’s unique primary desire.
We are what we do.
When we work out an interplay between desire and plot, the story becomes a moral, or at least emotional, testing ground. The reader is more fully engaged, watching to see how the MC will navigate the mine field of outer goal and inner need.
This is an advanced technique, but one that can reward both you and your readers. Your readers, because the story is deeper, and you as the author because you have so much more to work with!
You may already know how to use basic characterization techniques such as traits, appearance, world view and cultural constraints. You are probably also creating an MC’s inner landscape of desires and fears, strengths and weaknesses–and beyond that, showing the character in action and under stress.
The next step is to design the story events to hook your MC’s core emotional needs. Then set your character free to act within these exquisite constraints.
To ask Why is this character in this story? entails more work. But if an emotional and deep novel is what you love to read, then it may be the kind of novel you want to write.
Another aspect of characterization that treats the topic from a different direction: My post on Doubt and Desire.