Fill in the biography of your characters
Transform the description of the characters into a lengthy narrative about each of them, including all the relevant details: date of birth, profession, where they live, etc.
Here you can include synopses of your own story, but from the perspective of each of the involved characters. Most importantly, you can reveal how the character will be transformed by the end of the novel.
This will make your characters into real people, and sometimes they will make their own demands about how the story should develop.