Not so long ago I read an article at RPGnet about writing articles. It had some good advice, but I added something in the comments to the effect that it helps to set aside what you've written for a few days to a week and to read it aloud when you return to it. The problem is that you know what you meant to say and how you meant to say it, so when you proofread it yourself you hear what you meant to say; but if you can distance yourself from it by a few days you'll have forgotten enough of it that you're more likely to see what it actually says on the page than what you meant to write, and if you read it aloud you'll slow down enough to notice things like dropped words or awkward phrasing that your mind otherwise will fix on the fly when reading silently.
I don't do any of that with forum posts, for obvious reasons, and sometimes mistakes slip through; but then, I think to some degree having done it for my articles I've learned some of the mistakes I commonly make--I frequently drop the "y" from the end of "they", for instance, so I know to watch when I'm typing "they" that I not drop the "y". Proofing your own stuff that way can help you spot your common mistakes, and so improve your writing generally.
As to the use of sarcasm, you might want to devise a marker for it. I think that [sarcasm]no one ever misunderstands what I write[/sarcasm] works, but you could shorten it to [sarc]yeah, that's obvious[/sarc] if you prefer. (I'm assuming that those bracketed words will appear, since this form does not recognize BBC code but limited HTML, so brackets aren't significant symbols.) If you're really lazy, $and of course we know you're not lazy$, you could adopt any symbol on the keyboard that doesn't have another obvious meaning so used, and just go with that.
--M. J. Young
