For a good story, character and plot must be intertwined. In other words, what does the character want? (Character) How does she go about getting that? (Plot) What goal does the character secretly want? (Character) How does he go about getting it? (Plot)
Even secondary characters must have motivations and purpose. If not, you must press that little old delete button. After revising my fantasy Star Opening about a dozen times over several years, I finally realized the main character’s brother had no reason to be in the story except for being an annoying little brother. He did not move the plot forward. Instead, he rather dragged on it. So after years of developing this boy, tending him, tweeking him, loving him, one afternoon I sat at the computer and read through the book with my finger on the delete key and he was g-o-n-e. Poof!
As hard as that was to do, how much harder would it be to delete a main character?
Intertwine your character’s thoughts, actions, emotions with the plot — not just what is happening around her, but every action done or thought or feeling she has to reach her goals.