A few months ago I submitted a 6,600-word story to a market that, at the time, was accepting stories up to 8,000 words. While waiting for a response to my submission, the publication's guidelines changed and and the maximum length is now 6,000 words.
Today my story came back with a note letting me know that the editor liked the story, reminding me of the new length requirements, and suggesting that I resubmit the story if I could cut 600+ words from it.
Cutting the first 300 words was easy. Cutting the second 300 words wasn't.
First to go: Dialog tags. All those "he said"s and "she said"s weren't necessary. Many were cut.
Next to go: Imprecision. For example: "A few minutes before six, he..." became "At six, he..."
And then: Holy crap. At this point it becomes a paragraph-by-paragraph, sentence-by-sentence, word-by-word line edit.
But I did it and the story is on its way back to the editor.