"Writers" come from the intellectually snobby, yet stupid school of "I'm a WRITER, if I wanted to be an editor then that is what I would do." Good writers on the other hand believe that if they do the editing then there will be one less thing to pick apart and this is true, it also makes for a better story. Example, one of my pet peeves are typos (that and spiders, ohh and those strange little seed things at salad bars and that idiot on the bus... whoops back on track) Where was I? Oh, yes; typos. A lot of writers who write for pleasure, heck a lot of writers that write professionally, just use the handy little spell check under tools on their word processor. This is generally a good idea, I even use it myself, except for one thing; that spell checker is dumber than a bag of hammers. I'll prove it. Write two sentences, change a word in one of those sentences to a homonym (No, Fred, that is not a nym that is aroused by other nyms, will you get back to your sheep already?) For instance: This person had bad intentions. This parson had bad intentions. The first is just a general descriptor, the second is a specific descriptor. Heck, I was fifteen before I knew a parson was a priest, not some type of fish. There is nothing that ruins a story more than cruising along at a good reading speed, suddenly WHAM, you run into that brick wall of a missed misspelling. The reason the writer needs to do this is that a lot of editors have fallen into the same sloppy habit of just using that spell check thingy too. Who has the greater responsibility to their readers, the writer or the editor? Right the first time. Good, you're catching on. (Not you, Fred, personally I think you need a prison term, not a writing class.)
Another way for a good writer to edit their work is to, drum roll please, READ it! I can hear you now, grumbling in the back. "Of course, I read what I write. I love what I write. I have to read it while I'm writing it, right?" (Confusing writing that last sentence. Please allow me a brain break here. Okay I can press on)
Reading a story while you are writing it is not a good way to read it. You have ideas about where you want to take the story, what you want characters to say, etc. The best way to read it is finish the story, wait a week and come back to it. All sorts of things will pop out at you, if you sit there saying to yourself "Why the hell is this dude dressed only in yellow chicken feathers?" chances are your readers will sit there saying the same thing.