Picture This: How Pictures Work by Molly Bang
Not a photography book, but a simple intro to visual design.
These next three books are about the art of “seeing” and applying visual design concepts to photography.
Photography and the Art of Seeing: A Visual Perception Workshop for Film and Digital Photography by Freeman Patterson
Learning to See Creatively, Third Edition: Design, Color, and Composition in Photography
The Photographer’s Eye: Composition and Design for Better Digital Photos