Self-editing is one of the most critical parts of the creative writing process, and one of the hardest to master. Over the last year, I read and critiqued a dozen memoir and fiction manuscripts. All were excellent stories, worthy of publication. All contained at least two of the most common bad habits writers have. In all cases, the issues appeared over and over throughout the manuscript.
I do the same thing in my own work. My editor caught me using the word "back" over and over in my most recent manuscript. My characters stepped back, leaned back, turned back, sat back, looked back, and talked back. Thank goodness for the Find function in my software. I also look for really, pretty, and just. Other authors wear out actually, softly, and carefully.
It's not only word repetition, however. Other habits include overuse of a favorite sentence structure. Perhaps using series of three over and over, or connecting two separate sentence thoughts with a comma and the word "and." Or maybe it's the muse striking a bit too often, resulting in overly clever metaphors on every page.
Training ourselves to see our work with the reader's eye is difficult but essential if we want to produce a polished manuscript. It helps to let a manuscript rest for a few weeks before tackling the final edit. Another helpful approach is to ask your critique group to nitpick, and listen to them. Read a couple of good books on self-editing. One I recommend is Don't Sabotage Your Submissions by Chris Roerden.
Good self-editing can make the difference between acceptance and rejection when submitting to agents or editors. Learn to see your own work as a reader instead of the author. It's a different way of reading, and it works.