My all-time favorite figure painting book is Calvin Tan's Modelling Waffen SS Figures (Osprey Publishing, 2006(?)). Every figure in the book is fantastic: the final pictures of the first figure look like a photograph of a real human. And he shows you how he does it through well done, interesting step-by-step instruction. Granted, this is 1/35 scale, but wow! He uses acrylic paints, and gets stunning results. Although my results are nowhere near as convincing as Mr. Tan's, this book has helped me improve my figure painting dramatically, especially faces. I should add that I have no interest in modelling SS figures, but the techniques in this book will help with any figure. This book was relatively inexpensive, and worth three times the price.
The only book I know of that has decent 1/72 scale figures is Justo Mira's Diorama Addicted (AK Interactive publishing, 2013(?)). The dioramas in this book are fantastic, with moderately good step-by-step text, but he doesn't spend time explaining the figures.
I hope this helps.