From a writer's POV. Editing--a hot topic since the advent of self-publishing. First, I think doing whatever it takes to keep from publishing a book with glaring mistakes is of the utmost importance. Your name on that book will be associated with everything about it--from the cover... to the ending. If you put something substandard out there, the reviews will reflect it. You don't want to start out a writing career being associated with a bad book.
That having been said, it's fair to say that not everyone can afford a professional editor. So, can you edit your book yourself? Well, it' not advisable. For the most part, it's nearly impossible to do.
By the time you've written your book, you've likely reread it multiple times. That causes a problem. Your brain will read the words that aren't there--if you've missed putting in a word. You're brain will not register incorrect or clunky syntax. Missed punctuation marks, or the dreaded free-ranging comma will get right by. Your brain will see what you want it to see. You have essentially become blind to your own writing. It's not uncommon, and it's very real.
In lieu of an editor, at the very least, you should sign on with a crit partner, or a site that is basically a crit exchange. You crit the work of others and they in turn will crit yours. One I've read great things about is Scribophile
Whether you choose to hire an editor or not, there are some things you can do to help get over your blindness to your own work.
The best approach is to try to trick your brain out of stasis and preconcieved ideas of what's written in your story. One way to do this, and I've found it to work amazingly well, is to read your work out loud. You don't have to read it to anyone else, but you do need to speak the words. It gets a different part of the brain involved. Mistakes will jump out at you.
Another good way to trip up the brain is to change appearance of your manuscript. If it's in a doc. file, do a save as PDF or vice-versa. Or, change the font. Change it to bold, enlarge it, or highlight it.
Another time-proven way is to set the manuscript down and leave it alone for a couple of weeks. A couple of months is even better if you can stay away from it that long. It allows the brain time to forget what it thinks is there, word for word. You'll see it with new eyes.
Work on it in small sections. Join a group like (shameless plug here) Weekend Writing Warriorswhere you share 8 sentences at a time. It helps to teach you to be critical of writing--your own and that of others writers. There's a lot of help out there for free. And in the process of reaching out, you'll discover an amazing online writing community willing to generously help others. Weekly sign ups. Free. No long term commitments.
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