Sanderson's Laws of Magic
Brandon Sanderson, the author of Mistborn, The Stormlight Archive, etc. presents three points of consideration for fantasy authors. First Law Solving a problem through magic depends on how well the readers understand the magic. You cannot simply have vague magical powers and then use a wizard to enchant problems away. That would amount to deus ex machina, an unsatisfactory read at best, a betrayal of the readers at worst. Second Law Limitations are more important than powers. ...