Mastering Composition - techniques and principles to dramatically improve your painting, by Ian Roberts. Reviewed on WC here
. I recommend that you borrow this one before you buy it. I found Ian's book incomplete and flawed but his "5 picture planes" was my starting point for visual design. Reading his book was my lightbulb moment. I invested 6 months of hard study with little time for painting to find that starting point. It may not work for you, but it was an epiphany for me.
It's out of print, but Rex Brant's, Seeing with a Painter's Eye is my current number one design book. In used condition, it is still quite affordable. If you are looking for a gallery of paintings, this book is not for you. At 123 pages, mostly black and white illustrations, I only wish Rex had produced a larger book.
Tony Couch's "You Can Do It", is about 50% about composition and design. Tony is an Edgar Whitney student and this book is a wonderful compliment to Edgar's "Complete Guide to Watercolor Painting". Edgar's prose and compound sentences may be dated in today's sound bite world, but there is a gold mine worth of information about composition is his slim book and it's still in print, but be warned, there are few colour pictures in this book.
Jo Taylor's "Watercolor Wisdom" is a watercolour painting book, but Jo packs a lot of design including some design exercises into her book. Very well illiustrated. I suspect that Jo was either a student of Edgar Whitney, or influenced by is book.
The Artist's Guide to Composition by Frank Webb, is a YAEWS (yet another Edgar Whitney student) combines the examples of 24 artists to illustrate composition and design. There are at least three editions of this book around all with different titles. I think the earliest edition was called "Strengthen Your Paintings With Dynamic Composition" and the latest being "Composition for the Painter". I only noticed slight differences between the first two titles. I haven't seen the last title, so I can't comment of it, but from the description here
, it would appear to be a revision of the previous publication. YMMV