So You Want to be a Wizard by Diane Duane

From chapters.ca:
Something stopped Nita's hand as it ran along the bookshelf. She looked and
found that one of the books had a loose thread at the top of its spine. It was one of those So You Want to Be a . . . books, a series on careers. "So You Want to Be a Pilot, and a Scientist . . . a Writer. "But his one said, "So You Want to Be a Wizard."
"I don't believe this," Nina thought. She shut the book and stood there holding it in
her hand, confused, amazed, suspicious--and delighted. If it was a joke, it was a great one. If it wasn't...?