This infographic and article capture several of the commonly misused words I see.  It’s and its are tough for some people.  Remembering that the apostrophe replaces letters or a word helps me.   It is a (or it’s a) ball.  The dog chased its ball. You don’t need an apostrophe after 1980s because you haven’t taken anything out, but if you refer to the decade as the ’80s, you need the apostrophe. I.e. (that is) versus e.g. (for example) and assure, ensure, insure are frequently confused.  I thought the explanation of “that” vs. “which” was  interesting – if you take “that” out, you  completely change the meaning of the sentence.  Nice reference piece for writers.