"You must kill your darlings."
I read that line somewhere, I think Hemingway wrote it once upon a time. I think it's a great line. Here we got a majority of your editing worries pretty much summed up. You must kill your darlings. For me, this is really hard to do since I can't really see which darlings I need to kill. We're talking about writing by the way, just in case you were flailing in the wind there for a second or two.
I guess you could say I'm too much in love with what I wrote down that I don't see anything wrong with the story except for the glaring spelling errors. Tunnel vision. I see only what I want to see and move on. Since I started my blog and thanks to friends like Stewart Sternberg and Chuck Zaglanis, Susan Miller and Christina Rundle (and of course everyone else out there who leave comments)my sight has been growing wider and wider. Sooner or later I'll see the whole picture, and wouldn't that be grand? Yes. It would be totally kickin!! Okay that was dumb. Moving on...
Proof readers come in real handy here. Chances are one of them are most likely going to find the errors you missed. But even with proof readers one must be wary of grammar and structure and making sure you've got the right word where it belongs.
So you've found something that really doesn't contribute to the story you're trying to write. A word, a sentence, even an entire paragraph, whatever, it's just not working. If it doesn't and you or your proof readers see it, then toss it. Rework it. Kill you darlings...and gain control of your writing.