Writers know that they should be constantly reading. It is one of the universal pieces of writing advice shared in nearly every book on writing craft. To be a good storyteller, you need to be a good reader. Of course, fiction writers should read widely, both within their own genres and beyond, to have a good sense of what is already out there and what the conventions are, but reading nonfiction is equally important.
Many writers think of nonfiction books only in terms of research for a specific story that they are trying to write. If you are interested in writing Regency romances, you find books on the history, conventions, and trends of the time. However, nonfiction is useful for more than just targeted research. Writers are encouraged to read fiction widely, beyond their own genres, and I would encourage you to treat nonfiction the same way.
In reading nonfiction widely, I have found that nonfiction gives great insights on:
How societies work
Nonfiction can show how our societies work, how people's social rules, culture, and government all intertwine and affect what people do. I recently read Stacy Schiff's book The Witches, about the Salem Witch Trials. Schiff explains how Puritan values, rivalries between neighbors, and the stresses of life in an early settlement all swirled together to lay the foundation for mass hysteria. Even if you have no interest in the Salem Witch Trials, the book excellently shows how that society worked, how the right combination of elements could tear a community apart. This interplay between social rivalries and larger cultural and religious undercurrents is something that all writers could benefit from understanding, whether you are writing about 17th century witches or futuristic colonizers of a new planet. Understanding how societies work is important.
How people work
Nonfiction, biographies in particular, show us how people work. I've mentioned already in my post on audiobooks, that I am a huge fan of biographies. A good biography provides a full portrait of a person, both the good and the bad. I recently read Frank: The Voice by James Kaplan and am currently working on the sequel, Sinatra: The Chairman. In the book, Kaplan shows both Frank's absolute tenacity in pursuing the things he wanted, but also how that unflinching resolve and inflexibility could hurt the people around him. Frank Sinatra is undeniably an iconic figure, one who looms large over our culture. Much of his story has passed into legend, but Kaplan separates the man from the myth and presents both his accomplishments and his failings. For any writer, it is a master class in how to create characters that are compelling, charismatic, magnetic, but who can also be callous, demanding, and self-centered. People contain multitudes and no person is wholly good or wholly bad. Biography can help you see the shades of gray and contradictions in people, even our heroes.
How settings work
Nonfiction can also show us how settings work, how where we are affects what we do. Of course, this applies to books that veer towards psychogeography, like Peter Ackroyd's London: The Biography, but it can also be found in books that focus on people in a specific time and place. One of my favorite nonfiction books in recent years has been Devil in the White City by Erik Larson. Larson's book focuses on the preparation of Chicago for the 1893 World's Fair and the simultaneous rise of H.H. Holmes, one of our nation's most prolific serial killers. Larson explains how Chicago was the perfect place for Holmes; Chicago lured in people looking for a fresh start, for new opportunities. It was a place where it was not uncommon for newcomers to be swallowed up by the city, never to be heard from again. Larson juxtaposes the building of the exhibits for the 1893 World's Fair with the building of Holmes's hotel, which came to be known as the Murder Castle, and shows how the city of Chicago fed into both triumph and tragedy. Setting isn't just some white backdrop you place behind your story and forget, it has real and concrete effects on the people who live there and the actions they take. Places have an energy and a character that is all their own.
The Salem Witch Trials, Frank Sinatra, and 19th century Chicago have little to do with the story I am currently writing, but that doesn't mean those books weren't worth reading. Nonfiction can help to give writers a better insight on the world around us and the people that inhabit it, allowing us to create worlds that are more textured and believable. Do yourself and your writing a favor, don't neglect nonfiction.