In Stephen King's writing book, he says he normally cuts about 10 percent during the editing process. I've just finished the third draft. I went from 63,584 to 59,547. I just wonder if I've cut enough.
Key word here is "he." Stephen King normally cuts 10 percent, not every author.
Some over-write, and cut 50 or 75 percent. Others write it perfectly the first time around, and cut nothing.
You don't need to take him literally. There is no percentage. Just do what you feel is right. If something looks superfluous, cut it. I find that perception improves with time - if you have the time put the draft aside for a month or so and then read through. You'll find you're looking at it from a bit of a distance and you've gained enough objectivity to start seeing what you need to see when cutting. Ask yourself as you read whether the writing accomplishes anything - does it move plot onwards, create atmosphere, provide character insight via dialogue or introspection, set up character dynamic and so on. If it doesn't, chop and/or edit.