Envisioning Physical Appearance
Getting a firm grasp on what your character looks like can make him more real to you and to readers. Sketch out some thoughts about how the character looks, including hair color, eye color, height, weight and any unique features such as scars or tattoos. You also might consider how the character dresses and what this reveals about his lifestyle or occupation. For example, a character who's a model might be slim and wear high-fashion clothes, while a working-class mechanic might never go anywhere without his ball cap and muddy boots. Consider experimenting with changing these aspects of your character to see how it would affect your story, such as making him younger or older.
Hearing the Character's Voice
Dialogue doesn't just serve to advance a story's plot; readers can also learn a great deal about the characters through how they speak. Through dialect, vocabulary and communication style, the way a character talks can reveal the region he comes from, his level of education and his general attitude toward others. Include a section in your character sketch about the general way the character talks -- whether he speaks with an accent, tends to mumble or uses incomplete sentences, or constantly uses bad language or offensive slurs. Then, consider how the way the character talks to others might affect the way additional characters in the story see him.
Digging Into the Past
While the main focus of your story might be the characters' present conflict, knowing your character's back story can give you insight into what makes her the person she is today. Think about what your character's childhood was like, her relationship with her parents and siblings and any significant experiences that shaped her attitudes and beliefs. You also might consider what deep secret your character harbors, including why she thinks of it as shameful, what she's done to hide it from others and what could possibly happen if the secret were discovered. Perhaps the character is a drug addict trying to tow the line in her work and home life, or has a criminal past she's trying to cover up.
Discovering Goals and Motives
Ultimately, your story's conflict hinges on the primary objective your character wants to accomplish. Another part of your character sketch should deal with what your character wants and what is at stake if she doesn't get it. For example, your character might be an aspiring actress who has left home for Hollywood to try to start a career in the movies. Her family doesn't approve of her ambitions and has told her that if she leaves, she won't be welcomed back. Therefore, she has a lot to lose if her career fails. In your character sketch, develop the idea of what your character's goal is, what her motivations are and what obstacles she might face throughout the story as she seeks to attain her dream.