Garr Reynolds is a guru of good presentation design (aka the Zen of PowerPoint). I believe that the points he makes about good slide design also holds true for good book design when the page inlcudes an image and limited text.

For Garr's top ten slide tips see:
http://www.garrreynolds.com/Presentation/slides.html

Below, see Garr's examples of "before" and "after" slides. How do they differ?