Many years ago, when Jeff Ray was encouraging/mentoring me to be a Bible teacher, he gave me a book to read that helped my get started. It's called "I'd Rather Die than Give a Speech" and it's in our library. He bought several copies to give out to new teachers like me.
Even though it's not about teaching Bible, it is about overcoming nerves and learning some tricks to be able to present any kind of material well.
Help yourself to a copy if it's still in the library, or you can borrow mine.