You always hear about what has to be removed. Usually unnecessary stuff that doens't contribute to the plot. How about the opposite? How do you know when your story is lacking something? Say, more description, chapters, characters, or elements in the plot.

Sometimes I'll write something where there's a few paragraphs of buildup, then a "whammy line" or two. I wrote a quick example, pretend it's a climactic moment from a bad YA romance. She wrung her hands together, staring at her chipped nails, her calloused fingers, and the motor oil stained...