It might have been either a Scholastic or Weekly Reader children’s book, from either the late ‘60s or early ‘70s; but I might have just stumbled onto it in a random store.
I think it was a small, thin, hardcover book with a primarily medium-blue cover.
I think it had a relatively simple title, like Magic Spells and Potions, or something like that, but I can’t remember.

What I do remember clearly is my favorite spell in the book, which involved going into the forest and finding fern “seeds” with which to acquire the power of invisibility.