2) Develop skills that are hard to get outside the university
Your first temptation will be to fill your schedule with courses on fascinating subjects. Do this. Some of my fondest memories are of history or psychology classes that opened my mind to new places and ideas. But don't forget to also use university to build your technical skills.
By technical skills, I mean specialized knowledge that is hard to teach yourself on your own. I put things like math, statistics, ethnography, law, or accounting in this category. These are topics where you need a knowledgeable guide plus the hard commitments of a course to get you through hard material. Often, these skills are also basic building blocks for many lines of work.
For anyone interested in law, public policy, business, economics, medicine — or really any profession — I suggest at least two semesters of statistics, if not more. Data is a bigger and bigger part of the work in these fields, and statistics is the language you need to learn to understand it. I wish I'd had more, both as a management consultant and then as a researcher.
Even if you don't use it in your job, you'll use statistics in life. It's hard to fully appreciate the average New York Times (or Vox) article without knowing that language. And, frankly, when you're 30 you might care about the research on pregnancy, or the research on diseases and drugs when you're 60. It would be nice to have a basic understanding. Once you learn it, you'll be surprised how much of what is written on data is wrong.