Everyone has their own rules for writing.. here are just a few of mine.
1) Layer. No person in reality is just one thing. Not just “The Funny Guy” , just “The Villain” or just “The Love Interest”. They aren’t always happy, disagreeable or kindhearted. People have lots of facets so give your characters dimension by letting them have lots of sides that we get to see. Where you come from and how you were raised have a huge impact on who you become. Carefully layer details that create a rounded character.
2) Relationships. People do not exist in a vacuum and neither should your characters. They have families, friends, lovers and enemies. How do they relate to each other. Even if you never type the words “He was in love with her.” His actions should show the reader the relationship between the characters. These relationships create emotion. It’s easier to relate to the hero and you might want your reader to side with them but that doesn’t mean you don’t show the dynamics of their relationship to the villain.
3) Desire. Everyone wants something. Know the character’s motivation. If you know that it will be easier to pick how they will act and what they will say. Desires show what your characters value and what matters to them. Even the bad guys have a reason they are bad so let us see how they justify themselves.
4) Fears. Everyone fears something. Fears can help show a character’s history, their vulnerability and their overall outlook. It can also be a good way to humanize an otherwise unlikable character. Believable fears also give your heroes something to overcome making them more dynamic.
5) Variety. Tropes are tropes for a reason. You might not be able to completely avoid them so use them to your advantage. There are four humors or four main personality types for a reason, they cover the majority of the personalities that exist and give every one some one they can relate to. You don’t want all your characters to be exactly the same unless the premise of the story is that we are in a world that lacks individuality. Use the humors to your advantage and should how they complement and conflict with one another.
So those are the things I try to keep in the back of my head while I’m writing.
Who is this person? Where are they from? What do they want? What scares them? How do they relate to the people around them or from their lives? What type of person might relate to them?