Most of my insurance litigation focuses on writing persuasive briefs and letters. Given that focus, I read nearly any credible book on writing, in particular but not exclusively legal writing. Here are some of the best: The Winning Brief, Bryan Garner; On Writing Well, William Zinsser (who spoke at my undergraduate college’s commencement); Writing to Win, Steven D. Stark; Making Your Case, Bryan Garner and Antonin Scalia (which also delves into argument creation and selection); Writing Persuasive Briefs, Garvin Peck (available used only); Edit Yourself, Bruce Ross-Larson, and Mightier Than The Sword, C. Edward Good (with my favorite chapter title: “Compound Prepositions; the Compost of our Language” All succinct and worth your time