Make them different
Regular readers will know I like to be able to break a character down to the very basics. When you write your story, you have to be able to quickly bring to mind that character and how they act. A simple sense of who the character is really helps give you clarity.
But it can also help you avoid what is an all too common problem: all of your characters coming across the same in your story.
The big test of character is not how great your description is. It’s if the audience knows who these characters are in a single story. In a single scene. They should. Every time. Your characters should be that clear. And how do we do this? Through action. Through how they tackle a situation, react to the unexpected, respond to pressure. So you need to give them situations, the unexpected or pressure.
And you can test this. Give your scene to someone who doesn’t know the show and ask them to describe the characters. Do they get it right? If not, what can you do to fix that?
Here are some things you shouldn’t rely on to make your characters different: funny voices, catchphrases, colours, different tools or weapons, racial stereotypes. None of these things are a substitute for actual personality and the last one is right out.
Know who your characters are. Make them different. Then make them clear.