The Davis series "Art Education in Practice" includes Marilyn Stewart's
user-friendly "Thinking through Aesthetics." My students like this book and
it seems to help them get a grasp on the topic.
An older book that stimulates aesthetic thinking is "Puzzles about Art: An
Aesthetics Casebook" by Batlin, Fisher, Moore, and Silvers (St. Martins
Press). This book has aesthetic scenarios to contemplate.
I have used other more advanced books for senior-level and graduate-level
aesthetic courses, but these two have worked the best for beginners.
I think what Diane is suggesting for a thread of discussion is the
aesthetics of visual culture which would likely be difficult for beginners
until the understand the basic concept of aesthetics in general.