"Writing Economics" (Harvard Guide), Neugeboren & Jacobson

From the Preface: Across the broad range of topics that interest economists is a unique approach to knowledge, something common to the way all economists see the world. Economists share certain assumptions about how the economy works, and they use standard methods for analyzing data and communicating their ideas. The purpose of this guide is to help you to think and write like an economist.

Writing Economics (pdf)