Final answer:
The first clue for Mr. Griswold's game involves the strategy of hiding something in plain sight, as illustrated by the metaphor of a novice versus an adept player in a puzzle game. This sets the tone for players to seek out the obvious in their search for the hidden item.
Step-by-step explanation:
The first clue for Mr. Griswold's game in the book Book Scavenger stems from a quotation that discusses the strategy of hiding something in plain sight. The passage describes how an adept player of a puzzle game would choose words that stretch across the map in large letters because they are less likely to be noticed due to their obviousness.
This concept is analogous to the Minister hiding the letter underneath everyone's nose in Edgar Allan Poe's story.
This metaphor for the strategy employed in the game is the first clue to finding Mr. Griswold's hidden item. In the narrative context, the clue points to something being hidden within plain sight, leading players to seek out the obvious rather than the obscure.
Further consideration of the provided quotes indicates that players might need to look closely at common items or books that might ordinarily be overlooked, much like the books Dagget is examining in the third passage.