Grammar is not supposed to be some arcane cult with a punitive intent. I love seeing the range of issues that people raise in questions to Word Court, and tracking down answers that require original research. The trick is to try to put the piece aside for however long it takes you to be able to see it as if you were just a reader, and not the writer of it. For my own part, the only way I know of to hasten this process is to submit the piece someplace I care about. But then, unfortunately, it's too late to change what I've written in time to improve its chances of being well received.
Fiction is a special case.
In fiction, grammar doesn't matter, unless the character in whose voice the story is written is meant to be educated and proper. More often what's important is the authenticity of the voice. I do like to think that my new book, Word Court , would be helpful. The American Heritage Dictionary might be helpful, too, because it has excellent usage notes. Off duty I read mostly fiction, by a wide range of authors.