I also try to read newspapers and magazines that survey a wide range of areas. And I switch up the periodicals I read every so often rather than stick with the same one for years. For the past year I've been reading the New York Review of Books, which discusses books on a hundred subjects. In the past it's been a selection of foreign policy or current affairs journals, or ones about the arts. Or just a diverse Twitter feed of news items.
The other way is finding ways to spend meaningful time and relationships in new places. I'm fortunate that my work brings me to another developing country every so often, and each new place changes the way I think about development. Likewise, back when I was a management consultant, working in new industries and firms made me challenge old beliefs or come up with new ones. Volunteering in organizations did it too. Wherever you go, being a "tourist" doesn't cut it. You need local embedding, even if only for a few weeks or months.
Christopher Blattman is an associate professor of political science and international and public affairs at Columbia University. He also blogs about higher education, addressing topics such as choosing between master's programs, how to get a PhD and save the world, and if you're ever too old for a PhD.