7) Go to places that are unfamiliar to you
Use a summer or a school year to live abroad, ideally a place completely different from home, where you'll come to know local people (and not just the expatriate community).
When I was a student, I didn't leave Canada or the US until I was about 21. One day I realized I couldn't find Portugal on a map, and this shamed me into reading some history and taking a trip to Europe.
I wish I'd spent more than 12 weeks abroad, and I wish I'd stayed longer in one place. Coasting through youth hostels at the pace of one country a week does not really teach you about another life. It wasn't until I started working on research projects in India, Kenya, and Uganda that I started to learn a great deal about the world (and myself).
I'd also encourage people to get outside their comfort zones. When I got to Europe as a 21-year-old, I was so anxious and inexperienced that I found Eastern Europe and even Spain too intimidating and scary. I stuck to more familiar territory.
Ten years later, I unexpectedly found myself working in a war-torn corner of Africa. And that's my career today. I don't recommend it to everyone. It's not necessary to be worldly, by any measure. But I encourage American students to get away from English-speaking countries and Western Europe. Here's where it also makes sense to learn the language.