To add to the previous posts: I think one of the things which is crucial in college is to figure out for yourself how to understand the world, how to think about things, how to frame questions, what is important, etc: basically, how to think. Now, this is more difficult than one might imagine. I would suggest two strategies.
First, do choose a major. I knew many people whose education (even if supposedly carried out in one department) was really quite unfocused. You should try to take enough courses in one specific subject that you really start to understand its depth. This is a subtle thing. After one course or two, you have some idea of what sorts of questions people in the field ask, and what sorts of skills they have, what problems they are trying to solve and how they solve them, but this is necessarily still quite a superficial understanding. When you work up to tutorials, attend a few seminars, write a junior paper or maybe a thesis, your understanding will be quite different. You should be able to really situate this endeavor in the broader context of human attempts at understanding the world: Why is this kind of investigation important? Why do people devote their lives to it? What are the major contributions and why? Intense engagement with some intellectual project, even if it is one which ends up being orthogonal to the rest of your life, will inevitably serve you well.
Second, find people who you really admire and take courses from them; if possible, do projects or write papers for them, go to office hours. If things click, you may have found a mentor; in any case, there are not so many impressive people in the world, and one always learns from encountering them -- both about the subject and about life. When I say admire, of course, I don't necessarily mean agree with. But one of the interesting things about academic work is that someone who has been thinking about language for forty years will have deeper understandings every year (of course, how this manifests depends on the person). Whether or not you want to be a professor yourself, you have an opportunity, for these four years of your life, to hear the fruits of their labors, their years of thought and study, and to debate, question, investigate it yourself. So choose these people well. Personally, I would advocate choosing some fraction of courses (maybe your electives) based on the fact that there is a very interesting professor, in pretty much any topic in which you are reasonably competent.
I would also add: Cultivate the habit of listening attentively. Whatever you do outside of class, if you have made it up and to the lecture hall, train yourself for those 55 minutes to completely focus on what is being said -- to be totally "on," completely engaged. You should be able to walk out and give a coherent summary of what was said. Don't daydream or drift in and out of total focus. If you don't feel comfortable asking questions in class or it is not appropriate (large hall...), you might jot down questions in your notebook (say, 5 per lecture -- interesting questions), to keep yourself sharp. This is a skill which very few people have on average, but it is common to most great people -- CEOs and politicians as well as serious academics. And it takes a lot of practice. Four years is a good start. :-)
