My own definition of good fiction is pretty simple. If a story pulls the reader in so successfuly that the words as individual entities no longer matter, it's a success.
There are many factors that go into constructing fiction that can achieve that end. A simplistic list would be: character, plot, language. I've spent some time here talking about issues specific to one or another of these three cornerstones, and I'll continue to do that, but just at this moment I wanted to say something about mechanics.
If the idea is that you want your reader to fall into the story, you need to avoid things that will interfere with that delicate process. Anything that draws attention to the mechanics of storytelling will work against you. Spelling, punctuation, the way the text looks on the page - these things are irrelevant to the story, but not to the experience of reading.
As a professor, I tried very hard to read first for content, regardless of how badly mechanics had been handled. I made the decision to do that because I didn't want to discourage students who had something interesting and innovative to say. There's nothing worse for the creative process than a reader who refuses to really read. Imagine a kid bringing home a watercolor she is proud of, to have the parent's first reaction be something like oh no, look at the poor quality paper you're using. It's a short sighted parent (or teacher) who focuses first on the mechanics.
In publishing, editors don't want to be bothered with mechanics, and they have no patience with writers who take liberties. Most probably a masterpiece or two has been lost to the public because the manuscript was so riddled with mechanical problems that no editor would bother with it. So my simple rules for handling mechanics:
Spelling. Do not rely on your spell checker alone. Spell checkers get things wrong all the time. Make a list of problems that reoccur in your writing and double check for them. There are some kinds of errors that drive editors (and many other people) so absolutely crazy that you are well advised to triple check for them. I personally know people who seem to be capable of murder for the inappropriate use of an apostrophe in the word its. In order to save such over-caffeinated types from a case of the fits and give your manuscript a fighting chance, make sure that you don't use it's when its is called for.
Punctuation. You already know how I feel about exclamation points, those little daggers, those pox upon the nation. What you don't realize is that some people, many of them editors, get worked up over things like serial commas and when to use a semicolon. You don't have to look very far on the web to find raging arguments about punctuation, which says to me that some people have too much spare time, if that's the best thing they can find to argue about. I absolutely refuse to be drawn into discussions about punctuation, although people have tried. Once a friend called me late at night to say, hey, you've got a PhD in linguistics, you can resolve this disagreement for us: is it the Jones' house or the Jones's house? To which I said, You dope. Go away and find something interesting to wake me up about. Puncutation, like bell bottoms and hair styles, is a matter of fashion, and is constantly changing. Pick a way to do it, and be consistent. Your editor may not like it that way, but as long as you're consistent you should be okay (until you run into a Copy Editor with an Attitude, but that happens down the line).
Form. This is the simplest part, but people tend to resist. When I teach creative writing I make clear on the first day that I want all work handed into me in exactly the same format: courier 12, one inch margins, double spaced, plain paper. No negotiation, no wiggle room. I have had undergraduates hang their heads in sorrow at the idea that they can't show me the truth depth of their creativity by means of their font choice, and to them I say what I'm saying here: if you find yourself experimenting with fonts, you're avoiding writing. Get back to it. Courier 12 is the only font I use in manuscripts, because it's very legible. It's the only font I'll ever use in manuscripts. You may hate it, in which case you'll pick another non-descript, very legible font and stick to it.
Finally, don't confuse a well-formatted, clean, error-free manuscript with a story. Good mechanics -- like a beautifully wrapped present -- goes to waste if the box is empty.
So I've been thinking a lot about my list of favorite female protagonists, and then other female protagonists that I don't like as much, and I've come to the unavoidable conclusion that I like difficult women. Because I am one, you'll conclude. Maybe. It's true I have this lovely magnet you see here in a prominent place on the notice board immediately to the left of my desk.