All things serve the story.
Easy to say, hard to put into practice. As writers, we’re all in love with every word we grunt-and-push out of the glob of meat between our ears. We dote on them as though they were children, for that’s what they are. Writing is creative, and creativity is an act of birth. You’re bringing something into the world that wasn’t there before. Something that is made up of equal parts of yourself and the experiences you’ve suffered.
Every word of dialogue, every description, every lovingly-crafted villain is a child you’re sending out to suffer. But not all of it is necessary. Not all of it has a true purpose. Sometimes, you’re writing just to write. Sometimes the words are just words.
Your dialogue: it’s crisp and sharp and totally cool, just like the best dialogue should be. But like the dialogue of all the best movies, you need to ask yourself “does it serve the story?” Does it create good character? Does it give you insight into who they are? Does it forward the story? Your description. Does it paint a vivid scene? Did you spend three days finding just the right metaphor to descript how the sun-dappled leaves of the two-hundred year old oak in the front yard of your main character’s wave like babies learning bye-bye? And does it matter to the story?
The story is equal parts character, dialogue, and entertainment. Your story should be compelling, your characters should be real, and your dialogue should be a function of both. Elmore Leonard said that he began to find success when he started leaving out the parts that people skip. His writing took on a very tight, very spare quality- but the dialogue was razor-sharp, the description was just enough to give a sense of place, and his stories were simple: two people at odds, usually. Two separate, real characters with two separate goals and two separate, diametrically opposed directions.
Every word has to serve the story.
Having said that, there is a world of learning that has to be done to know what to keep and what to let go, and I’m sad to tell you this if you didn’t know already: it never stops. There’s never a point at which a writer just automatically knows what needs to stay and what needs to go. You have to struggle all the time, all your life, all your work must be honed and sharpened and continually checked.
It never ends.
It does get easier. It gets easier the more you do it. So… go do it.