Posted by Emperor Tiberius:
I give every fic I write two proofreads; one just after it's completed, and then a second before it is posted. But it's true, whenever I review a completed fic later on, I find, invariably, that errors still got through my filtering process.
It is indeed very difficult to spot errors when they're your own. Have you ever tried having someone else proofread your fiction, though? I have six friends who read my stories critically before I post them publicly; only three of them read for grammar/spelling/typos, but even so, that's enough to ensure that the story is pretty clean before it goes up on TrekBBS. I would highly recommend this approach, if you can find people generous enough to spare their time.