The "misuse" of the word "literally" has received a lot of attention lately. I put "misuse" in quote because there are those who feel strongly that unless you are, in fact, what is said, it's wrong. (I happend to be in that group.)
But there are others who feel equally strongly that no one could possibly think the person is really a fish, that his head really exploded when he was faced with a difficult math question, or that he really ate 1,000,000 M&Ms, and therefore, it's simply a colloquial but acceptable intensifier.
When someone says "When I saw that math problem, my head literally exploded" or "My God, was Sarah a pig. She ate, like, literally, 1,000,000 jelly beans!" I do wince. It's as bad as "very unique" to me. Many other people have no problem with it.
In your academic and formal writing, certainly avoid it. It's a personal choice how you handle it in speech.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.