Of all the editing techniques I've read of, stumbled across or worked out for myself over the years, the single most useful one is reading aloud; ideally to an interested (or at least tolerant) audience. A passage can be one I've looked at a dozen times before, but when read aloud it leaps off the page and demands to be improved in some way.
At the simplest level, reading aloud reveals typos that have resisted any amount of proof-reading. And it's particularly effective for finding words that are repeated in uncomfortably close succession. The eye can be determined in seeing just what it wants to see, but when the text is slowed down to the level of the spoken voice, many such hidden flaws are revealed.
It's particularly unforgiving, and particularly useful at detecting, what I give the editing abbreviation of "lw" to: long-windedness. Again, the eye can skip over such passages, but when said aloud they're revealed in all their tedium. And they get cut in the very next editing phase.
I like my prose to have a certain rhythm, and reading aloud is a good way of checking this. Even though most of us have gone beyond sounding out the words as we read, dialogue in particular does flow better if it's in a form that it's actually possible to speak. It's an effective way, too, of checking that the various speech patterns of the different characters are consistent.