Some Notes on Revising a Manuscript: Refining the Prose
Refining the prose is best saved for last; you don't want to spend time polishing something that will later be cut.
If any words don't support the plot or characterization or tone or mood, they should be changed or removed.
If you repeat descriptions or thoughts too many times, the reader is more likely to skim, so you might want to cut some, or change them to make them more interesting.
It's usually better to have strong verbs than to have too many adjectives and adverbs. For example, " John went shakily down the steps, almost losing his balance" can be edited to read, "John teetered down the steps." This goes along with avoiding the passive voice, which in most cases distances the reader from the story.
Paragraphs each address a single main idea. An additional way to create paragraph breaks is to look for the most powerful sentence, and either end or begin a paragraph with that sentence. Ends and beginnings stick in the reader's mind more than middle sentences. Don't waste them.
Look for words you tend to repeat over and over, either dull, bland words that can be cut, or really distinctive words that will begin to grate on the reader. Keep a list of the words you overuse, and when you're done with other revisions, use the search function to see if you can change any of them. Note that these words change over time; as you conquer one, another will crop up in its place.
Read dialogue out loud to check the rhythm and see if each character has her own distinct speech pattern. Can you tell them apart without attribution? If not, consider making at least one character have more distinctive speech, for example always being curt or always being wordy.
This is what I look at while revising. It sounds like a lot, but some of these line items are instinctual now, and I'm generally addressing more than one of them at the same time. It just takes practice.
Kate Elliott, a science fiction and fantasy writer whom I respect very much, works on one new craft problem with each novel she writes. I think that can be applied to learning revision, as well.
Coherence and storytelling.
The Art of Letting Go: Finishing the Novel.
Related post: Writer's Voice.