During your time at university, you're definitely going to take classes that you did not expect to take. For example, right now, I'm taking Intro to Archaeology. I've learned a lot about the evolution of primates to humans. I had no idea how difficult it is to define homo sapiens as homo sapiens, or how interesting the progression of tool usage is. The class has given me a different perspective on religion and diet. I look forward to all the other interesting, unexpected classes I have to take in the next few years. To come across classes that feel like pleasant surprises, I recommend looking for general education classes in disciplines that you have at least a slight interest in. Sure, it's nice to have an easy gen ed -- but make sure you're at least a little invested in the material.
University is a unique environment. Every day there are people within a mile radius of you who are experts in the field that you are pursuing, and the density of information around you is probably at once of the peaks in your lifetime. Building strong relationships with the people who hold this information is the easiest way to build a stronger understanding of your field. In order to do this, I recommend actually attending your classes. Don't be afraid to ask questions during lectures, and definitely don't be afraid to go to office hours. Attend office hours to ask questions and always be sure to introduce yourself. Knowing someone's name inherently builds a stronger relationship than you might expect. It may seem silly -- this professor has a million other students too! But the key here is that out of those million students, very few are likely to introduce themselves, and very few are likely to continue to attend office hours.
Adjusting to university can be a difficult process. Most aspects of your life go through a large change. The best way to deal with this is to know that there's a whole campus of people around you who are going through the exact same changes. Building relationships with your peers is an invaluable way to navigate this adjustment period. In lecture, ask people next to you quick questions. Introduce yourself and keep a dialogue going. Ask if they want to work on homework together, or if they want to get lunch after class. Personally, I think the most valuable relationships you can build is with peers in your major who are at least a year above you. Join a club related to your discipline and make friends. They know what professors are good, what classes are good to take together in a semester and what classes will be difficult to take together, whether it's worth it to declare a minor, and so on. Don’t be afraid to ask them for advice.
I was unprepared for the amount of time it takes just to get around. We have a pretty big campus, and a significant amount of your day ends up being taken up by getting from one side of campus to the other. This may seem silly, but when you have a jam-packed day, sometimes having a bike makes life easier.