Ask yourself, why do you want to write this story? What is your passion? What theme do you want your readers to take away from your story? What is the premise of your story? Describe it on one sentence using the what-if formula. What if a flawed protagonist encountered a problem and had to overcome the flaw to solve the problem? Whatis one flaw that prevents your protagonist from solving his or her problem? Later, you can give other flaws to your character, but the main flaw is what you will structure your story on.