As an extension of your number three: Take all the math and linguistics courses you can without shorting your major - these are among the most generally useful

As an extension of your number three: Take all the math and linguistics courses you can without shorting your major - these are among the most generally useful and hardest to learn on your own courses. By linguistics, I mean phonology, syntax, and semantics, our knowledge of how language works; languages are also well worth learning, but Berlitz and Pimsleur are at least as good as university courses at teaching them. Also take all the lab courses associated with your major - they will give you more tacit knowledge, knowledge of how things actually work, than theory courses. Note, I'm mostly self-taught (including calculus), these are the kind of things I wish I had learned in school when I was there.