I love to see things properly spellchecked (and I'm a bit of a compulsive proofreader) but I'm not sure it would work with their plain text input, when we can't even find autotranslate entries if we haven't got the start of the correct phrase.

If you're writing large amounts of text in advance, possibly do that in Word so you get spelling and grammar checked. Try to take the time to re-read what you've written before you post, to pick up obvious mistakes and to make sure you're happy with it.

Beyond that, the most important thing is to understand the rules yourself and do your best to stick to them. Capitals, apostrophes, spelling, full stops and commas to break up sentences and convey pauses in speech. Use the autotranslate to check game terms (type the beginning of the word and hit Tab). Pay attention to your own writing and just maybe others will see that it's easier to read and makes for better writing.

As for learning those rules... read! See how other authors use them in published books, or other writing you consider well laid out and easy to read. Check things you don't understand.

Good proofreading is more complex than just letting a machine insert the correct spelling.