Just start writing. Short stories, love letters to nobody, summaries of movies you've seen or books you've read, complete with some of what the characters said. This will give you practice describing things and dialogue. If you have an idea for a book (which I assume you do or you wouldn't have asked) get started on it. Just get writing!
If you want some education to back it up, an English degree will be a big plus. Some agents won't even consider working with an author who does not have a Master's of Fine Arts in creative writing degree. These aren't necessary (untrained writers, including me!, get published all the time), but the education will improve your writing, inform you on the writing and publication process, and (more importantly) give the agents and publishers an indication that you are serious. You can also make use of networking opportunities through the school you attend.
EDIT: Don't get me wrong: write because you love to write. Just remember that the business end of writing and publishing is just that: business! And a tough one at that.