You have a story you believe in. You must create characters readers will also believe in. So where do you start?
The first step is to separate your major characters from your secondary ones. The major characters move the story. These are the people most effected by the events and climax of the story, and most likely to have a significant impact along the way.
Start with your protagonist. As the world-builder you must know a lot more about this character than your readers may ever see. Depending on your own personality, decide how they look (description); personality traits, specifically how they interact with other “types.” Friendly with those they know; standoffish with strangers; enjoy the company of others; loner; smartest person in the room; smart with tech, dumb with people? Really get into the inner workings of their mind.
What do they wish for? What do they most fear? What secret do they hold closest? What person do they love? Secretly love? Hate? Secretly hate? What is their moral basis? Trustworthy or self-centered? This could go on forever, but the more YOU know about your protagonist, the more real they will become when you write.
Know their education. Know friends they left behind and those they still have from childhood. What led them to their profession? Are they happy? What changes do they long for?
How do they see their world and how does the world see them?
Get into details. Nervous ticks. Catch phrases they use and over use. How they dress. How they would prefer to dress. Accents, dialects.
Note: DO NOT try to write accents and dialects unless absolutely required to “humanize” a character. You can say someone has a British accent without italicizing every sentence, or placing ‘ and removing every “h.” The reader will fill in the accent, or ignore it.
The simplest way I can give you to develop your leading characters is begin with stereotypes relative to your specific genre. Stereotypes exist because followers of particular styles expect certain things from their characters. You layer those stereotypes with your own interpretations of their personalities. Make the individuals unique and rememberable, but not so odd no one will relate. In the beginning, they may be little more than a shell. The events and conflicts occurring in the story line will add nuance. In fact, it is better to allow a character to grow on the reader by watching them grow from experience, than to shove a fully-formed personality down their throat.
I use rewrites to complete my character developments. My first draft sets my story, timelines, and where I want to take the reader.
I have a basic understanding of how I plan to get from the first page to the climax. The rewrite begins with each major conflict (Change) within the story line. By the end of that scene, I want the major characters involved to experience their own change. I want the reader to discover more about them because of how they deal with the situation and how it changes them. Hopefully, I make them more sympathetic or more despised.
Get out the notebooks or warm-up the computer, but write the name of your major character at the top and start building! Remember, only a small part will get shared openly. This part of character development is for you.
Step 3 will cover character arcs. Character art for Don Foxe at donfoxe.com.