When I first started working at my current job, the HR department emailed everybody what they considered a fun game— find all 10 spelling and grammar errors in a page of text, and you could win a gift card.
I found fourteen.
OK, so at least two “errors” were more in the realm of stylistic choices— Oxford commas and so forth— but I won the gift card. And then I became my bureau’s copy editor.
My style of editing is fairly instinctual. I’m looking for one thing above all else— does it make sense? Would a reasonably intelligent and half awake member of the target audience be able to understand it? I do look for ambiguous language, typos, grammar errors, and logical consistency, but I’m also looking at language rhythm and flow.
Sure, you can study this. You can sit down with a grammar [0] and styleguide and memorize the rules. But the best way to learn what good writing looks like is to read lots and lots of good writing. Read it obsessively. Read it until the rules of language have seeped deep into your bones.
Also, read bad language [1]. Try to figure out why it is bad. How would you improve it? Is it confusing? Does it ramble? Does the logic flow? Are there spelling errors? Is it utterly lacking in capitalization, punctuation, paragraph breaks, and other bourgeois affectations [2]? Your goal is to become on of those douchebags. You know the kind I mean. As your edit-fu grows strong, and for extra credit, try turning your attention to any newspaper’s Op-Ed pages.
Editing your own work is phenomenally difficult. It is impossible to edit and compose at the same time, so don’t even try. They use physically different parts of your brain, so you’ll have to do each in a separate pass. You may find it useful to use a different technique for each pass— for example, I compose on paper, but edit on the screen, then proofread again where possible on paper.
Also, you will have to create a physical and mental distance between yourself and your work. After you have finished writing it, stick it in a drawer for a while. For a blog post, a couple of hours. Term paper or feature length article, a whole day. Your novel? At least a month.
Your best editing tool will always be another person. Not a close friend, not a family member, not someone who wishes to spare you hurt feelings. An honorable enemy is best [3]. Someone who is willing to be brutally honest, explain in exacting detail where and how you’ve screwed up, and assassinate your children in front of you. Someone who is willing to tear your ego into little tiny shreds and stomp them into the mud. Choose for your editor the nastiest, most vicious drill sergeant you can find, with all the gentle sweetness of a hungover wolverine. Learn their favorite drink, because you’ll be buying a lot for them.
Read their comments very, very carefully. Then stick the whole manuscript back into the drawer. Get mad. Rant, rave, wail, moan, gnash your teeth, tear your hair, and clutch your pearls. Tearfully explain to your very best friend that your sunovabich editor Just Doesn’t Get It. Get drunk and have the same conversation with the smelly guy sitting at the far end of the bar.
A week later, when you’ve finally gotten over yourself and the hangover has abated, pull your magnum opus back onto your desktop and reread your editor’s comments. Figure out where they’re right, and why they’re right, and how to fix it.
Congratulations. You’ve now achieved the rewrite.
[0] Allow me to recommend The Deluxe Transitive Vampire: A Handbook of Grammar for the Innocent, the Eager and the Doomed by Karen Elizabeth Gordon.
[1] The Internet being a particularly rich trove.
[2] Dear Random Netizen: Typing in all lower case was individualistic and stylish when e. e. cummings did it. On you, it just looks like you don’t know what the shift key is for.
[3] Think the Poker Game of Mystery Writers on the TV show Castle. They’re always eager to tell Castle he’s full of shit.