With specific reference to editing narrative passages, some people do find little tricks that help, and one that I now use is to read my work backwards (I mean paragraph by paragraph). It's a bit similar to a well proven fact that most people can copy a drawing much more accurately by doing so while it is upside down. They are no longer seeing what they think the picture represents, rather more objectively what it actually is. And I've found that the "read it backwards" technique helps me see much more clearly the structure of a paragraph outside the context of the story unfolding in my head. Not so applicable to the feeling that a whole story is stale, but might be worth trying more specifically when passages seem to have become simply a jumble of words. I'm sure lots of people have their little tricks, but that one definitely helps me.
Proofing is my biggest issue. I blame it on my analytical mind. While I should be able to use it for finding errors and blunders, it enables me to "fill in the blanks", to read what's not there. Especially dreadful: edited sentences, where the edit left out the other half of the sentence...
Posting it on a website or using a different font helps.
Anyway, back to the original question: I started writing my novel #1`August 2006. I finished it August 2007, and a friend read it. Her judgment was: "good story, I love your characters, however there are issues..." She (editor and teacher) made me think about the craft and about publishing. I had to start a new project a month ago, because I couldn't make myself go back and work on it
again. Burnt out, tired, stale... but after working on my new project, things are living up. So, maybe that's what is needed: put it away for four weeks, work on a new wip and then go back. I wouldn't do a six-months hiatus as Stephen King recommends... then the trail would be cold for me.