Sometimes, you need external help. You need to ask someone to edit your work because you have seen your words one time too many and you're never going to spot errors when you know exactly what you meant to say in the first place.
When you get to that point and you have someone else help you edit your work, make sure that you don't just accept and move on. Absorb everything you can from this gift that you've received.
Really take a look at those edits.
Did every one of your semi-colons have to be changed? Is your dialogue full of filler words? Are you redundant with adjectives?
If you get help from an editor, don't only let them help you with this one piece. Take a real look at the work they've done and try to catch those errors in your future work—no help required.