The majority of the time, editing means removing the fluff--getting rid of unneccessary words, sentences, and paragraphs (or, in my case, the occasional page or chapter).
However, there is a point where too much can be taken out or you need to enhance a passage to enrich the story.
My first piece of advice when editing is what I've called macro-level editing. How does it look? How does it sound? Does it make sense? This is where large block of writing can be eliminated.
Macro-level editing is also where block of writing can be added. Do you have any descriptions? Are you telling instead of showing? How about dialogue?
Micro-level editing involves the intricate pieces of your writing. The individual word or punctuation.
What I recommend is to read slowly, out loud, and continuously ask yourself questions like:
Is what I'm thinking about in the story being drawn out in the words?
What could be done to enhance the story?
Where is the story lacking?
These questions at least could help in editing your story. Does anyone else have any tricks they'd like to share, on what's worked for them?