There are people who stay on message — and then there’s Ryan Serhant.

The celebrity real estate broker, who gained global fame for his appearances on Million Dollar Listing New York, is hyper-focused, direct and as polished as the gleaming surfaces of the mega-penthouses he sells in Manhattan. Not a bad look when you’ve just published your third book, a guide to branding oneself and one’s company.

Titled Brand It Like Serhant: Stand Out From The Crowd, Build Your Following, and Earn More Money ($30, Hachette Go), the book takes readers through chapters designed as a step-by-step program that includes identifying a core identity, advice on using social media, and exhortations to “shout it from the mountaintop,” i.e. confidently and emphatically promote oneself. It includes exercises at the end of each chapter and even includes photos of Serhant modeling outfits and showing poses that do and don’t...