After you edit a piece you have written and you can
not "see" it any further, it is time to put it aside. When sufficient time has passed, you can edit it again.
And rest. And start the whole process over.
At some point, you may reach an impasse: you are not able
to come up with any further changes. Now is the time to submit the piece to a person whose editing skills you trust.
One of the first decisions the editor makes will be, is the piece worthy of his/her time? If it is not, do not be dismayed.
The time you spent writing was not wasted. Your efforts made you a better writer.
When an editor
has read the piece and you look at the suggested changes and see what works, you make the necessary adjustments. The
author always has to trust his/her instincts. And rest, again.
At every point in this process, you
must take a deep breath and relax and accept the results. This preserves your sanity.