Basically the editors writing the book suggest cutting repetition, not only of words but of feelings and scenes. Then intended goal, of course, is to get out of the way of your story. They phrase it as 1 +1 = 1/2. The more you 'explain' an emotion or any point, the more you diminish it.
Another great segment was on 'beats', or 'stage business' for actors or screenplay writers. It's how to break up dialog with actions. I do this already but I'll make sure when I'm doing revisions that I don't have too many paragraphs of straight dialog without there being some physical action as well. That segues into another bit on paragraph construction. Again, this is something I do pretty well, I think but it was good advice on how paragraph length can cause the feeling of a scene to speed up or slow down. (the same is true of sentence length). The final chapter was on 'voice', both of your characters and of yourself. Voice is critical to any good writer. The book acknowledges as well that it's impossible to 'teach' someone to find their 'voice' but it had good advice on how to search for it. They suggest reading your own work as if you were new to it. (Yes, that's a tall order in and of itself) Then to underline any passages you liked and underline in a different color any passages you don't. The lines you like will lead you to discover your 'voice', hopefully. The lines you don't are places to ask yourself 'what's not working here?'
'Self-editing for Fiction Writers' was very accessible and full of good and hopefully eye-opening advice. I recommend it to writers of any skill level, even if you've mastered every trick and craft outlined in the book, it's still a good reminder of what to do and why.