Sanderson's Laws of Magic

From Wikipedia: Sanderson’s Three Laws of Magic are guidelines that can be used to help create interesting worldbuilding and magic systems for fantasy stories. These three guidelines should be used when writing a hard or soft magic system.

Sanderson's Zeroth Law
"Err on the side of awesome."

Sanderson's First Law
"An author’s ability to satisfyingly solve conflict with magic is directly proportional to how well the reader understands said magic."

Sanderson's Second Law
"Weaknesses (also Limits and Costs) are more interesting than powers."

Sanderson's Third Law
"Expand on what you have already, before you add something new. If you change one thing, you change the world."