If you follow the simple rules here, you'll do just fine. I see these errors every day. Yes, there are all sorts of magical incantations in grammar, intricate rules that most writers don't need to worry about. A lot of it is having a good ear and writing what feels correct...most of the time, you'll be right.... but these errors I've listed are so rampant that they have (unfortunately) entered the mainstream.

And certainly, if you ever have a grammar question, I'm happy to discuss and teach!