I have to agree with all the above about Carol Marine’s book! Really first rate and readable. I also like the Greg Albert book as well. Another book that I find valuable is “Creative Illustration” by Andrew Loomis, written in 1948 and reprinted in 2012. It has some excellent info on composition and ways of guiding the eye through a composition. I found some ideas on coming up with new subjects useful as well.
After all, the purpose of illustration is to get the viewer to look at your image, and this man was a true master at that. That point has really resonated with me. When competing for attention in today’s visually saturated world, we need all the help we can get to slow down the grazing eye and get it to stop and focus on our offering. Used copies available on Amazon.