A favourite tip from the archives:
A consolation: as you perform the necessary editing, it really hurts. "I love that line, it's such a neat bit, it's brilliant!" Brilliant isn’t actually enough--it's got to be brilliant, and have a place there. And oddly enough, you cut it, but in a weird way, it's still there. It’s gone but it hasn’t actually gone. It’s still there in your denser, and your richer and your better text. It’s in the texture. Books are palimpsests of your earlier drafts. So don’t be too disheartened because it's gone, because it isn’t really. Or to give you some Confucianism: what the pruning shears remove remains on the tree in its enhanced vigour. A good rule of thumb: if you have to think more than five seconds about whether or not a thing should be cut, that means do it. In the age of word processors, I’ve got a file called "may be useful one day," where I put things that are great and that I can’t bear to lose. I cut and paste and put it in the file, so at least it's there in case I ever want to go back and retrieve it. How often do I go back and retrieve it? Never. Not once. Which I feel proves my point.