You might ask, how do you do that? Well, although it isn’t easy, I can give you a couple of tips that may help. First, know your characters inside and out. What are their habits? Where were they born? What kind of life
did they live? These are the kind of questions you need to ask yourself before you start writing. The list of questions goes on and on, and the dossier you build on your character (and yes, I recommend that you create a file on your major characters for consistency, this is what some call a character bible or story bible) will be invaluable.
Now you might ask if I have all this information, my story’s going to get bogged down in superfluous details! Not true. Just because you have the information, doesn’t mean you have to have five pages of info-dump when you introduce the character. The information you create will help you know how the character is going to act and react to the situations in your story. It will build the depth that you need, and ultimately help you as a writer.
Here’s another tip…don’t make your protagonists goody-two-shoes, and don’t make your antagonists nothing but pure evil douchebags. The best antagonists I’ve read are sympathetic to the reader. Nothing creates internal conflict better than not knowing who to really side with when reading. Make your main character torn. They don’t have to be a neutral down the middle type, but require them to make hard choices, give them blemishes and they’ll shine in the eyes of the reader. Nobody is perfect, and readers will be able to see if you create one dimensional characters.
These are just a few things to think about when you’re writing. If you want a more in-depth look at the subject, I suggest you take a look at Orson Scott Card’s Character and Viewpoint, Donald Maass’ The Fire in Fiction, William Strange has a great blog on the subject, or even better, chat up Scott Johnson. He gave a wonderful class on character building at my graduate school and is a master on the subject. Now go write!