Here are some ideas I gave another writer who asked how to cut down a piece that is too long for today’s market.
How many characters does it have? Can any be combined into one character to do the job? Or cut entirely?
How many subplots does it have? For a novel over 90,000 words, probably too many. For a short story, zero is the correct answer almost one hundred percent of the time. (I’m talking about the average short story which is between about six and six thousand words.)
Is it too heavy on description–in today’s market, short is better, especially for short stories. Three lines maximum is often suggested as a good rule-of-thumb, but if you do fabulous descriptions, of course, you don’t want to limit yourself this way. Do be careful when writing short stories, though, not to have too many. Frequent readers usually expect short stories to be full of character and plot and little else, unless you’re writing literary fiction.
After looking at the big picture, you can go in and look at each sentence. Is it pulling its weight? Look for trailing phrases that can be cut. Often the words at the ends of sentences mean little or are redundant or obvious.
Next look at excess words, mostly modifiers, making the words they modify as strong as you can.
And if you’re done and still not down to where you need to be, either get someone who’s published to look it over and make suggestions, or hire a professional editor to do the job. Or both.