If you could go back in time and give your younger self one piece of academic or professional advice, what would it be?
Learn to really listen. When I say "listen," I mean: take the time to hear an idea or concept, think about it, and be willing to change your mind. Why is this important in academics and professional trajectories? I'll give you a few examples.
In school, I was sometimes a know-it-all. I remember a couple times where, instead of learning new material, I would just hear the parts that I already knew (and be pumped I already knew it), and then miss the important new information. Similarly, I would often answer a question quickly, rather than allow myself to be part of a conversation in which I probably would have grown and learned new things. Had I learned to listen earlier, I would have saved myself some embarrassment, and I would have had a richer knowledge about some important topics.
People are drawn to good listeners. My friends and colleagues who sit back and ask good questions, rather than talk about themselves all the time, seem to be doing the best academically, professionally, and socially. I would guess that this is because they are likable, so people will give them more opportunities and will think of them first. I also think they are successful because they've mastered the art of learning: asking lots and lots of good questions!
Lastly, being set on a certain professional trajectory early and not wavering from it is not necessarily a good thing. People who listen to new information and evaluate it might change their mind about what career they are preparing for. As you grow up you learn about more opportunities and career options that you might not have known about early on. Listen to people talk about their experiences, and learn from them. You'll be happy you did.
A favorite professor told me to "listen as though you will change your mind." Learning to listen in that way has changed my life, and it will change yours too.