To avoid creating flat characters (especially female ones) ask yourself the following questions:
- Is she authentic? She has to be a true representation of herself as a fully realized character. She may go through trials and tribulations, but she must not be flat or a projection of the need of another character and function as a plot device.
- Is she valuable? What they contribute to the storyline adds value. Period. If you take them out of the plot, it decreases the worth of your story significantly. Or entirely.
- Does she help drive the plot? Every character in a story must serve the plot somehow. If they just appear as window dressing, they won’t feel real to your readers. And they won’t hold interest.
- Is she easily replaceable? If she is, then you haven’t created a strong character. Character strength isn’t about heroics. It’s about the strength they add as a realized character to your overall story.
- Does she reinforce a stereotype? This can be tricky. What can happen is that a writer may create a character of the exact opposite of traits of a perceived stereotype and may inadvertently create a new stereotype in the process. If you feel you may have reinforced a stereotype, ask if she follows question number 1 and 3.