Ask yourself: “what’s their motivation? What does my character want more than anything else in the world?"
What to they most desire? Love? Acceptance? Chocolate? Peace? War? Friends?
Also consider the opposite. What will they do anything to avoid?
What scares them to death? Humiliation? disfigurement? beetles? pain? illness? poverty? parents ?
Usually, in the course of a story, protagonists will confront the thing they fear the most and overcome it in order to win the thing they desires the most.
In order to make your character and their story interesting, people will need to care about them - even if they are evil. Make sure you empathise with your character. Care about them and other people will too.
Now, once you have explored your character, think about what they look like and try and draw them based on the mental image you have created. It doesn’t need to be a masterpiece by any means. And remember that most popular cinema and TV characters are assembled from simple shapes: circles, rectangles, triangles, etc.
Make sure your characters appearance reflects their personality. Typically, physical traits like large eyes make characters appear cuter and friendlier, where as mean characters often have smaller eyes, and are usually large or disproportionate.
For more on creating characters - try here
