Read widely and voraciously. Seek out the best in the field. 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.