A lot depends on what your final goals are. Generally if you intend on going on in academia, i.e. earning a PhD and then doing further research, I agree with Dishsoap that getting involved in research is a good idea. Find something that can give you some hands-on experience so that you can interact with graduate students and professors and find out what the word is really like, and what the process of doing research is.
Make time to read about your own interests and pursue your own projects. Even if this is simple stuff like writing some code, or soldering a basic circuit together, it can go a long way to helping you figure out where your strengths lie and maintaining motivation over the long run.
Also make sure to have a backup plan. Academia doesn't work out as a long term career for the majority of people who start out in an undergraduate physics degree, so as you're going through your courses keep in mind that at some point you're likely going to have to apply for a job in the "real" world. So it will help to have skills and experience that will help you in that pursuit.