As I've been busy this week, I'll post a quick recommendation.
'A book on rhetoric' sounds like a tome you'd find at the back of a library, a foot thick, and in five-point font. Farnsworth to the rescue. He provides a concise guide to rhetorical techniques (or 'figures'). He illustrates each type and sub-type with multiple quotations, from Shakespeare to G. K. Chesterton to 18th-century politicians.
Half of this book's pleasure is recognition. Every other day we'll use a few of these figures, most of the time without thinking about it. That shows good rhetoric is not a fusty contortion of language better left in 19th-century classrooms. Good rhetoric is what we naturally recognise as good communication. But while we all can unwittingly dash out an epistrophe, it helps to know what an epistrophe is. Know rhetorical figures so you can strategically deploy them, rather than instinctually drop them. Know what they do, and where best to use them.
To anyone with an interest in expressing themselves well, or recognising good expression in others, I recommend this book.