It's a bit random, but: if you're not already in good shape (and many of us hacker types aren't coming out of high school), find where the gym is and learn what to do there, and go three times a week.

College is one of the first chances where you A) generally have free access to a decent gym, B) have enough control over your own time to set a workout schedule, and C) you're generally old enough that working out will actually do something for you.

Getting in good shape will have a positive impact on your energy level, but more importantly it does wonders for your self-confidence and self-image.