Here's a proposal: always leave one card in every Tarot spread face down. Why? Consider this definition of the future:

"It should remain part of the definition of the future that it is unknown; and therefore allowed to retain its proper mystery." —The Future is Tomorrow: 17 Prospective Studies, 1972

Substitute the word "divination" for "definition":

"It should remain part of the divination of the future that it is unknown; and therefore allowed to retain its proper mystery."