Editing comes in multiple types, and the definitions about those types will differ depending on whom you ask, but something needs to be borne in mind when self-editing:
Writers cannot judge their own level of effectiveness.
That's true for short stories, magazine articles, ad copy—all of it. (I know I've commented on this before, but this wasn't the primary focus of that post, and I want to be clear.)
Writers know what effects they intend to have on the reader. Those intentions affect how writers perceive their own writing.
So while I do believe that some writers can often accurately identify when a piece is effective, and that some writers can identify what prevents a piece from being effective, I do not believe that writers can trust themselves to identify how effective a piece of writing is.
That's why it's important for a writer to have betas, or a trusted "first reader"—one or more persons whose judgment they trust, willing to read their stuff and tell them if it works or not. (Or to tell the writers how their writing works. All of us sometimes come up with things that convey completely the wrong moods from what we intended.)
So if you try self-editing, bear in mind that you still will want at least one set of critical eyes going over your manuscript.
Some writers work best by only having one person be that reader. Others work fine with multiple betas, though betas will often give contradictory advice.
Personally, I find it particularly useful to have a manuscript read by someone outside my personal demographic (be it in age, gender, or religious affiliation), because my demographic affects my perspective. A reader who disagrees with me about life, the universe, etc., will be inclined to catch situations where I'm missing pertinent transitions.
For example, I discovered (after I published "The Corpse Cat") that many folks assume that an intimate relationship between first cousins is necessarily incest, not knowing that it's allowable per some municipalities and even by the book of Leviticus in the Bible.
There's no line addressing that legality in "The Corpse Cat". If I'd realized what a hang-up it would be for some readers, I would've sought a place where I could insert a brief explanation. As things stand, I'll be trying to (briefly) address the legality of it in the sequel to Destiny's Kiss (where Emris and Samhain appear again).
I'd thought I handled the relationship well in "The Corpse Cat". But not for folks for whom it's taboo.
I'd entirely forgotten that first cousin relationships were taboo for many people. I've been used to the concept for some years, starting from when I discovered that some of the folks I knew were married first cousins.
If I'd bothered to send that story through a first reader who didn't match my demographic—which was "people who know first cousin relationships can be legal"—I would've known that before publication.
Do you use one or more beta readers? Have you had situations where someone read your piece and got a completely different message from it than what you intended?