Rule #1 in editing anything is to take a break. Two weeks or more. Work on something else and let it percolate. You'd be surprised how things float up from the subconscious if you just give yourself some breathing room.
Rule #2 is to scrutinize your verbs. Are they active or passive? Did you say she "began to shout" or she "bellowed"?
Rule #3 is to track the sun. If your character goes into a building at noon you better make sure they don't exit the building in the dark unless they've actually spent that much time in there.
Rule #4 is to keep your head straight. In other words KEEP YOUR POINT OF VIEW consistent. And make sure you do not HEAD HOP mid scene or chapter. This kind of mistake is jarring for the reader. You should be consistent throughout.
Rule #5 is to read your manuscript, particularly your dialogue, out loud. I can't tell you how many mistakes I've found by ear that I missed by reading. You may feel silly, but do it. It works.
Rule #6 is to double check punctuation. Pay close attention to your quotation marks in dialogue. Make sure your periods, commas, and other marks are present and needed.
Rule #7 is to show not tell. Can you replace stated emotion with action that conveys that emotion. She was angry about writing the letter...or...She scraped her pen across the paper with staccato strokes, muttering through pursed lips.
Rule #8 is to slash that back story. Pepper the exposition throughout the chapters via dialogue or other narrative. If you have huge block of back story explanation then you started your story in the wrong place.
Which leads me to Rule #9. Make sure you start your story in the middle of the action. Just as the character's life is about to change. Most writers end up hacking away at the first or even the second chapter during edits.
The key is to "Save It As" your second draft so if you hate what you've done, you can put it back. Then just dive right in there and start slashing.
Any editing tricks you find work well for you? I'd love to hear about them. Until next time...Go Write!