When asked what it was about her story that caught her agent's eyes, debut author Marilyn Brant said, "I asked my agent that question and she told me that she found the story very human." (Marilyn's book, According to Jane, is in bookstores now.)
I think finding the heart of the story-the theme- the human part of a story is one of the most difficult things for an author to do. There are no rules for that. There are no use-this, not-that, kinds of things. Some people find the theme first. They decide they want to write about love and loss, or second chances or family relationships. Then they create a plot and characters around their theme.
I am not that "lucky." I usually have characters who pop into my head. I "see" a scene and the story starts. I have to write the complete first draft before I am aware of the theme or the heart of the story. Even then it can be fuzzy.
But knowing your theme- your heart is the only way to revise and market your story. You have to understand what it is your characters and you as a writer are trying to say. It has to be about more than character growth and emotional arc. There has to be an over arching theme. Oh, no, you say. I've finished a full book and there isn't a theme. Don't throw it out. There is a theme. It's hidden in your words and it's up to you to discover it.
My latest book, Mr. Charming, has the following themes of forgiveness and acceptance-self forgiveness (Jennifer has to forgive herself for the public demise of her first marriage before she can enter the real world.) Family forgiveness-(Kane must forgive his parents for dying and himself for living before he can create the change he needs in his life.) Self acceptance-that being human with flaws and imperfections is what enriches life and how attempts at perfection lead to isolation and loss. Heavy stuff for a romantic suspense-lol But these themes are universal and easily recognizable to your reader. They can immediately connect with your characters and your story. They are drawn to the human element- the heart of the work.
Once you can state the theme of your story- you can revise with an eye to that theme. Does this scene echo the theme? Does this paragraph enrich the theme? If so, how? If not-edit it out.
Once you know your theme you can market your work to that theme-in your query letter- in your back blurb- in your pitch.
Finding the heart of your story-what makes it human-will make the work shine with possibilities and create a work readers can readily identify.