I'm compiling a list of favorite/ recommended poetry/ flash fiction "how to" books and the book I'm presently exploring (again) is Robert Hass's A Little Book on Form: An Exploration into the Formal Imagination of Poetry (2017). Hass is a Pulitzer Prize Winner (and winner of many writing awards) and clearly demonstrates his skill as a writer. I will definitely include this book in my list of recommendations. It's quite an interesting book and I was rather surprised to discover that.