I try to base my revision on a re-reading of what I’ve done so far, imitating, so far as it’s possible, a first-time reader. That is, I try not to bring too many ideas about what the story is doing etc., etc. Just SEE what it’s doing. In other words, read along with a red pen, reacting in real-time as I go along, deleting, adding, etc. When the energy drops, then I know that’s where I have to really start digging in, i.e., turn away from the hardcopy and go to the computer. Repeat as necessary?