School.

If you're in college right now, and especially a top-tier university, try to meet as many people as possible. Don't miss this opportunity; your network will be invaluable once you're done with school. College is a great place to step out of your bubble and college admissions committees usually do a good job of putting a diverse group of interesting people in one place. Meet people from different backgrounds, countries, and majors. Even though you may not realize it now, you will one day need most of the people that you meet in school.