With a six-year background in editorial, Agent Heather Alexander of Pippin Properties summed up illustration notes DOs and DON'Ts recently on her blog in A Note About Notes
It's brilliant. Succinct. Helpful.
I especially like the idea of re-imagining them as "stage directions."
Take note. (pun intended.) And read the piece. It's well-worth it.
Illustrate and Write On,