The next deadline in my pile of calls for submissions is May 1. The call is somewhat outside of my usual bailiwick, but I might give it a try for the sake of stretching myself.
My edits mostly fell into four categories.
1. Extraneous stage business. When drafting, and mildly stuck, I often insert stage business such as drinking from a cup, fidgeting, etc. until I know what to write next. I cut most of that out later, as it isn't all needed. I keep a little for the sake of changing scene rhythm or indicating mood, that sort of thing. I also sometimes have too many steps when describing an action, for the same reason I suspect, so instead of having someone reach out or towards something, and then touch it, in edits I skip to the touching part.
2. Tangents. If I wander too far from the main topic, usually in dialogue, I rein that in when editing. Even if the dialogue is charming or funny. Unless, of course, I need more wordcount; then it's "characterization."
3. Too many words. This is the Strunk and White thing. I replace wordy explanations with pithy ones, replace a bunch of weak words with fewer strong ones. Also, see tangents.
4. Repetition. In drafts, especially when trying to set a mood, I tend to use a few words over and over. I eliminate some of those uses and change the others to more specific ones whenever I can. I try to make sure the words I use (usually verbs) are absolutely the most accurate and evocative I can find.
I'm not that systematic, of course. I do all of those things at once, usually working from the beginning of the story to its end.