When I begin to write a novel, I’ve already formed a picture in my mind about the story’s protagonist. I know the role that character will play, and I have a general idea about how he will interact with the other characters in the book. Those other characters will support and build my main character.
It’s important that whoever you create to carry your story to the readers has some likeable characteristics. Not that your protagonist must be a goody two shoes, but there should be some element that attracts readers to him. There must be some commonality, one that readers can identify with—it can even be a flaw.
Once I’ve formed a general idea about the fictional person, I begin to jot down a description, including physical characteristics, education, family, interests, strengths, weaknesses and maybe even some idiosyncrasies. As I begin to write the novel, I will make additional changes that either strengthen or make the main character more vulnerable.
As for the antagonist, he doesn’t always need to be the archetype villain. He or she can be somewhat normal, and posses only one flaw. However, that one flaw must be one that causes him to create the conflict every good story needs.
Supporting characters are born as my story progresses, or as needed. I have a “skeleton crew” of characters already in my head. Some will contribute greatly, while others may only be needed to create an important scene. After that, it’s possible they may never be mentioned again.
Whether your story is complex or simple, it’s necessary to maintain what I refer to as a character log. The log will contain information such as physical descriptions, how the characters relate to other characters, etc. It is essential that you keep the log handy by your computer. Refer to it often to ensure you keep your characters honest, meaning, “in character.” Update it often to guarantee your players are fully developed.