Well, I never did get all my notes typed up from the SCBWI-LA conference as I promised, but I can share one important bit of advice. This came from Cecilia Yung, Art Director & VP at Penguin Young Readers Group: "action, reaction, interaction." As I looked back over my portfolio, this bit of advice helped me tremendously. I saw that many of images could not be said to be "interacting" or even "reacting," so I know I need to work toward making my illustrations stronger.
Looking at Angela's painting of the boy reading (see below), we can definately find all three. There's action with the boy reading and wriggling in happiness; there's both reaction and interaction with the boy's eyes and how he holds the book. Good job Angela!
Hope this bit of advice helps everyone as much as it's helped me. Now, before I consider my work done, I "analyze" with those three words: action, reaction, interaction.