When you are describing a person to a third person, what are the things you talk about? The way they look, the way they dress up, the accent that they have, their favorite phrases; all of these come together to give you that perfect image of the person that you are trying to describe.
A character sketch can be one of many extremely useful literary techniques to create an image in the mind of a reader. It makes certain things synonymous with a particular character. It is therefore, possible to shock the reader by giving a twist in the narrative using the description of the character.
While writing this it is important to remember that it is a description of what makes the character who he or she is. It is not a description of the circumstances that made them who he or she is.This technique is very different from direct and indirect characterization which are the techniques most authors use to develop characters.
The Development Process
Writing a character sketch can be the easiest task that you can ever be set to, in case you are perceptive and have a keen power of observation.
It is important that a reader knows exactly what the character looks like. The reader should know what it is about the character's physical appearance that sets him apart.
Describe his limp, the birthmark on shoulders, her falling hairs, the lightening scar on forehead. These details will make it easier to relate to the character.
Another important thing that every reader should be given insight into is how the character behaves. This is imperative, in order to allow the reader a glimpse into the character's emotional and mental makeup. Everything that the character says or does will be done with a reason and the reader should be allowed to perceive this with ease.
At the same time keep some things open to interpretation according to the reader's imagination. If the main text is full of soliloquies and asides, then in a character sketch, include these. When you do this ensure that you mention that you are quoting this from the main text.
Third Party View
Another method of describing a character is to include in the description, what other people in the main text or novel make of this character. Their observations can go a long way in establishing the things that make the character you are describing, unique.
Other methods that can go a long way in helping you write a character sketch is explaining how others behave around this character, describing the environment that the character lives in, and the way in which the character deals with the conflicts in his life.
Writing this description can often give you a more rounded perception of why an author developed a character in a certain way, what he was thinking while creating characters in a story and why the character behaves in the way he does.