Concept. Composition. Contrast.
Concept: Your book cover should have distinct meaning that is quickly understood by the viewer.
Composition: The text and visuals that make up your book cover design should have dynamic relationships and balanced placement.
Contrast: Legibility should not be an issue and design elements should be easily discernible from one another with use of color and texture.
I focus on these fundamental principles to make sure you book cover is a success.