As anyone surely has realized, I use to produce plenty of typos, due to speed-typing on the keyboard without ever having learned it systematically. 9 of 10 errors you see in my words, is due to mistyping. Switching to Opera has started to lecture me a bit and may have made my postings less stressful to read, it has an auto-correction feature that indicates errors right at live typing. Rest assured, I did not mean to discriminate against English speakers - I produce as many typos when typing in German, too.
But occasionally I indeed fall for wrong knowledge of correct spelling. And one thing that totally confuses me time and again is when to use an "s" and when to use a "z" in words, for example "organising" or "organizing"? "Realising" or "realizing"? Is it always "z" in verbs, or is it mixed with some cases of using "s"? School is out for me since 27 years, and I cannot remember anymore whether there was any rule on this or not. And so I violently shuffle s's and z's and do not really know what I am doing there.
Any general rules?