Several months ago in a post on word confusion I suggested apostrophes could use a post of their own.
I don't really believe that.
So I'm going to throw some commas and semi-colons and periods in here, too. In honor of English teachers and grammarians everywhere. Can't you feel the love? I may throw in some capitalization, too.
Here's why apostrophes don't need a post of their own: it's not that difficult.
It's/its. The apostrophe goes into "it's" if, and only if, you are contracting "it is." That is all. No other time. "The window sparkled in the sun, its ancient glass throwing rainbows across the room." No apostrophe.
"It's a beautiful day." Apostrophe. It is a beautiful day.
Other apostrophes are used to denote possession. If you can say "Johnny owns that," you can write "Johnny's book." But please don't write "we have three Johnny's in our class," or "I'm writing three book's about grammar." Apostrophes are NOT used to create plurals. No, not even when you've gotten three As and a B. Anytime after the 1980s. No apostrophes.
Another thing I've been seeing a lot of recently is confusion between when to use commas vs. when to use semi-colons. Or periods, for that matter. Lot of run-on sentences enlightening the world these days. Look, there are lots of reasons to use commas: to set off parentheticals, create lists and set off names, for example. One thing they do not do in the English language, though, is end a sentence. When you get to the end of the sentence, add a period and capitalize the next letter. Don't throw in a comma and keep going. If you have a sentence, and then the next sentence is not really its own sentence, more a continuation of the first one, consider a semi-colon; it's often a good way to vary the length of your sentences, if nothing else. (See what I did there?)
More on caps another day. For now, start here: if it doesn't start a sentence and isn't a proper noun (name, for example), it probably doesn't need to be capitalized. Unless you're channeling a 19th century author instead of being a 21st century one yourself.