The Crowood Press recently released a new book which is bound to become a classic "figure painting" title, like those by Shepherd Paine, Danilo Cartacci or Mike Blank. Oh, and don't be discouraged by the title, the info and techniques described in this book is applicable to painting all figures in all scales, not just those representing WWI era.
This is partial text from the full article (usually with photos) at https://armorama.com/news/modelling-and-painting-wwi-allied-figures-from-crowood