I think it was Lisa who asked the other day if we give our attention to the forest or the trees when we're rewriting. I didn't have an answer then except for, "yes," but this week I ran into the same question myself. I am so deep among the trees right now that I simply have to back away, go back to the beginning of the manuscript, and take a look at the whole forest--which is to say, I need to read my book again from the start. Does that ever happen to any of the rest of you novelists? Or can you always just keep writing from wherever you happen to be?
The "trees," in my case this week, are the characters more than anything else. I need to make sure I have portrayed their emotions fully enough, and right now there's so much going on in the story all of a sudden that I'm not sure I have captured the depths yet. So I'll go back to the edge of the forest, and then keep walking up a hill in the distance until I can look back and see what the whole thing looks like. Then I think I'll be able to pick out the bare spots, or the ones that need pruning the most.
That's the theory, at least. :)