“Everything that doesn’t advance the plot or reveal characterization.” Now to pat myself on the back and throw my laptop in front of a train.
I never liked this shallow advice — as factual and aggravating as it is. Its distillation leaves out nuances in the determination. What’s the proportional focus of your story’s plot compared to its themes? What kind of character are you characterizing? What story are you trying to tell?
By your first draft’s end, the themes should be clear and the characters fine outlines in your head. Knowing these lets you jettison everything which doesn’t advance the plot (in accordance with the themes) or reveal characterization (relevant to the story).
If the theme is people can’t respect power they haven’t earned, the main character need not sporadically acquire their power during a protracted bank robbery turned hostage situation. What do the robbers add to the theme? It’d be better, and far quicker, if the power was tantalizingly offered to the main character by a person whom lost their life’s worth by ignoring the theme’s warning. Just because something advances the plot, doesn’t mean it did so in the most well-constructed, thematically appropriate, succinct way possible.
As for characterization it’s trickier because (in theory) everything reveals character. Every action, inaction, line of dialog, and thought expresses character. But what can be cut is every piece which doesn’t build upon the story. If the character is obsessed with ramen, ask what importance ramen has in the story. Do they compete in a ramen contest or run a fledgling ramen restaurant? If so, keep it, if not, don’t waste more than a short sentence on it.
If you can complete an entire story and upon your second draft you find the step up to subplots and character arcs you didn’t finish, then you’ve already shown they aren’t needed to tell the story. Salvage helpful story elements for the established narrative and ditch the rest. Any completed subplots and character arcs which don’t affect the ending can be discarded. They don’t need to conclude with the story but their lasting impacts on the characters and the world should be present at the climax and resolution.
Another sign to break out the scissors is when characters reiterate plot points to another character. If they talk line after line about something the audience already understands then switch to prose and say, “He told her about the night in the cabin and the mysterious silhouette in the window.” Additionally, the prose shouldn’t rehash the same, tired plot points, insinuating the readers are simple. This is a major issue with serialized works and multi-book series. If you write well enough to make the audience care, they will remember the wide brushstrokes.
Now the rule of thumb for your second draft is it should be 10% shorter than your first draft. The preceding advice won’t ever remove 10% of the story’s word count (unless you loved talking about ramen). There are more techniques available besides cutting, such as consolidation.
Say two characters reach a door which has two locks on it. The characters first go down one path and encounter a key on a pedestal. Angie, grabs the key but triggers a trap dropping out the floor between her and Jacob. Jacob throws a rope and tells Angie to grab it so he can hoist her to safety. This agitates her history of being let down by those close to her and she’s reticent to put her life in his hands believing he’ll take the key from her and drop the rope. After some talk back and forth, she puts her fears away a moment and grabs the rope. Then they travel another path and grab the second key.
Getting the first key has tension, escalating stakes, conflict, and character development. Getting the second key is flaccid because nothing of significance happens. All the things which made the first key grab good could be added to the second key but what’s the significance? Are the character rolls flipped? Does Jacob get the chance to challenge his own flaws? I’d cut it on the spot for being repetitious.
However, the conflict Jacob goes through could play out simultaneously with Angie’s peril. If Jacob needs to learn to drop his selfishness and help others then the character growth of both scenes can be melded together. Rather than have them walk down a new path, reach another room with a key in it, describe the room, take time to establish narrative stakes, set the tone, and create a mini three act story inside the scene; Jacob’s character conflict and resolution can be fitted into the previously established scene. Make the door have one lock as most doors do.
My favorite place to dent that 10% is in the prose. On average a sentence has twenty words. On account of any first draft’s unpolished nature, most sentences can be shortened by at least one word. This easy step will get you to four, five, or six percent depending on your prose style. Editing this post, I reduced the count 5.9% (65 words).
From sentence to sentence, apply the duh method. I’ve said it before but it’s something I remind myself of every once in a while. “She nodded her head.” Duh, as opposed to what? “He sat in the chair at his desk.” Duh, what else would he use? “She shouted loudly.” “He whispered quietly.” If there’s a vestigial verb modifier, change the verb. “He ran fast,” becomes “He bolted.” If, “He’s even better,” then it’s also true, “He’s better.”
A normally small issue which can kudzu if left unchecked is M. Night Shyamalan dialog. Characters don’t have to separate every contraction to give their words importance. It will strangle the life from your story; please mow them down.
In your story, large changes to particular chapters and small cuts throughout can keep the pace up and pare down the word count by the rule of thumb 10%. What you choose to cut is up to you but what needs to be cut will raise bile in your gullet. Everything should have a purpose and that purpose should help you say what you want to say.