I was going to post this Mallard Fillmore comic just because the comic funny and about grammar, but it reminded me of a rule: Don’t use apostrophes for plurals.
But there are two exceptions that you might get away with: plurals of numerals and plurals of abbreviations. You don’t need to write plurals of numerals very often, but when you do, it’s okay, but not necessary, to use an apostrophe, and the tendency these days is to use the apostrophe less and less.
So, for example, referring to a decade, write “the 1960s.” If you really want to, you can write 1960’s and you’ll get away with it. Buying house numbers? The neighbor of the Beast bought two 6s and an 8. Or is it two 6’s and an 8?
Moving on to abbreviations; the rule is do what is easier to understand. Walking into the vacant space, she said, “Wow! This office has enough room for three AAAs.” Or three old-fashioned AAA’s.
Usually I leave off the apostrophe, and no one has fired me for it yet.