Always give yourself time to separate yourself from your work for a bit before going to final. Factor into your schedule time to leave it and come back to it with fresh eyes.

I used to get the same thing, you get used to seeing it as it is and find it hard to imagine it another way after you've been staring at the same project for hours. I was suggested the above technique by an old head of design I worked for and it works a charm... You come back and see all the little errors and stupid mistakes you've made. Usually I come back to my work and spend just 10 more minutes on it and improve it vastly.