I struggle with this endlessly. What I have found works pretty well is to write the whole thing, do one sizeable revise on my own and then if it's a short piece, post it on the SYW boards and get some feedback from others here. Or if it's long, just post a portion of it.
It helps to get feedback from others, especially if you are just starting out, because it is easy to get stuck spinning your wheels . You may struggle with what you think you need to revise--when in actuality there is a bigger hole somewhere else. Feedback can help you focus by identifying specific things that need to be revised, rather than you trying to attack the whole thing all at once.
Also--the more you stare at your own piece the harder it is to see all the "good" in it. You might start to see all "bad" and then you are prone to start hacking away when you really don't need to.
I have definitely over revised something before, so I would recommend that you save all your revisions incase you ever want to go back and see what you changed. Sometimes you might want to change it back…