The correct form is "dos and don'ts." My biggest pet peeve is when people say, "do's and don'ts." They add an apostrophe to the first word, but not to the second word. So they are basically using two different rules at the same time. If you happen to think words like that need an apostrophe, at least put the apostrophe s in each word and not just one word. Off the top of my head, the only pluralized word that needs an apostrophe is when you are talking about your grades on a report card as straight A's. This is only to differentiate it from the word "As."