One lesson I've had to learn the hard way, but I warn students about all the time, is that over-editing is worse than not editing at all.
Tightening is good and healthy, and it usually involves dropping the fluff words and moving toward more powerful verbs and nouns. But when I kept editing for word count, dropping and dropping every word I could find that wasn't critical, I lost both flavor and breath to the work. Lesson learned the hard way!
So, how do you know when you've over-edited. When it sounds mechanical. When the spirit is low or void. When the USC band could tap out a marching tune to your sentence rhythm. Sometimes it's better to lose a sentence, or even a paragraph, than to over-tighten every sentence on the page.
Another pressure you might befall to is over-edit for pacing. Now, I love a quick story that gets my heart jumping. But you cannot maintain that break-neck speed every paragraph of every page. You have to let the reader breath, so again let your phrasings have some down time, slowing the pacing so there's a few extra heartbeats between words.
Reading your work out loud doesn't always produce the best edits, but it will help you identify when your work is too tight, too strained, too fast, or just too brittle.
And, if you made the same mistake I did and over-edited your work, the cure is to go back to a blank page and write the work from memory. Maybe that sounds too hard, but even just a few pages from memory here and there, or even a few sentences, and you'll find that natural voice again.
Good luck and good writing, Angels!
Your Editor Devil