Internships are very important. Do several internships at different types of publishing companies to learn the differences and similarities. Try for a large company like Houghton-Mifflin, but also a small local publishing company. Expand your experiences to learn as much as possible, then you'll have a better chance of finding the job that best fits your passion.
Go. To. A. University.
Seriously, not a college, not a seminar, a University. There is so much to learn, and you'll be able to keep up with the Industry faster in one.
Take Journalism if you're undecided of what you wish to Edit for (Magazine, Books, Newspaper, etc.)
Take History, if you're going to take your career to an academic level. I suggest you look at job listings to see what publishing houses are looking for in an Editor. The Industry changes seasonally.