Read the classics, both SF and other. I wish I'd read more of the non-SF classics when I was in school. Practice, practice, practice writing. Writing is a craft that requires both talent and acquired skills. You learn by doing, by making mistakes and then seeing where you went wrong.
Short stories are a good training ground and an easier market to break into.
If you're wondering about a course to pursue in college, and you think you want a career in writing, choose the school that you think will give you the best all-around experience. Much of what I learned in college I learned outside the classroom. Write from the soul, not from some notion about what you think the marketplace wants. If you can stand the thought of not writing, don't attempt a career as a writer. It's difficult and often painful.