1) Keep up your chops for the instruments you don't play as often
Going down an orchestral path, playing extremely hard marimba solos was not really a focus of mine. Before going to college I did have decent marimba solo chops, but once I arrived there, I didn't use them as much, and they slowly deteriorated. If I could do it over again, I would've kept up as many solos as I could and tried to learn a lot more.
2) Answer as many questions as you can, then ask the rest
I loved asking questions in college. The one thing that has changed is that, now, I search for answers more by myself than by actually asking someone else. On average I can answer or find the answer of at least half of the questions I have, and then I can ask an outside source or teacher the rest. Take charge of your education, answer your own questions, confirm or challenge those answers, and then ask the ones you cannot answer yourself. The learning really happens in the process of you finding the answer, not just entering in the question and getting the answer from someone else.
3) Jam out with your friends
The one thing I wish I did, and that I now do with one of my former classmates, is jam. Just either playing duets together, or playing stick control to music, or even improvising on world percussion instruments. A big part of playing musically is feeling free enough to take chances or to make strong choices, to play off of someone else's ideas or energy, to have and share your own ideas. Playing with other people in a supportive environment, and even outside of the structure of college was really helpful to me and I wish I did it more often.