A character with a voice means more than having them participate in some dialogue. Characters need to sound different from each other too.
Creating unique characters are vital if you want your readers to remember them outside of the covers of your book.
There is a lot of pitfalls to fall into while creating a character. Some I’ll list in short here, with these all and more also gaining their posts for more in-depth information.
No matter what the characters do, the world and plot stay the same. If the protagonist insults someone in one scene, that same one might not be willing to help in the next. All actions have consequences, not only to the positive.
The character interactions with the world around them should affect other characters and the world alike. People’s relations might change, the world moves toward devastation, and the villains gain allies because our hero pushes them away.
No goal or motivation
Related to the consequence-lacking issue, this is when the protagonist is just along for the ride. They never take action; they make no decision that pushes the plot forward. They are the lense which we as the reader see the world, but they barely interact with it. All they do is react, defends themselves against external forces.
It is the secondary characters that make the decisions, that makes mistakes that lead the plot forward. Or the villain keeps doing things so that the hero has to react.
Using archetypes or stereotypes might seem like an attractive idea to get started. But make sure it is only to get you started, and that the characters don’t stop there.
No character is the mentor with only that in their mind without becoming no-one to the reader. Don’t fall for the stereotypes of real people—gay people are not always colourful and flamboyant.
Mary Sue or flat characters
While a stereotypical character is terrible, so is a bland character. They can also be the same thing. Mix it all up a bit, the mentor-character might also be a comic-relief character, and the hero has to figure out what is a joke and what is real advice. Suddenly you went from a stereotype to the more dynamic person.
They all seem the same
One of the most important thing when creating characters is to make them stand out against the cast that is in your story. The reader needs to be able to follow who is who while reading. Names, descriptions, and personalities all factors into this.
There has to be something unique about each character in your book, both for the reader to remember inside the story—but also after reading the last page.