I agree with everything Alex Miller said, especially the part about becoming a newspaper journalist.
Not only because you will learn (with the help of experienced editors) how to research and organize and write stories of varying lengths, but also because being a journalist will provide tons of fodder for your own writing. When I was a reporter and editor, I often would work on an article and think, "That has the elements of a great fiction story."
Also, journalism requires interacting with many people whom you would otherwise never meet. It takes you to places outside of your everyday experience and provides a useful, real-world education in how and why people think and act they way they do, including their motivations and passions, successes and failures, hopes and delusions, and all the other things that contribute to great writing.
As for getting your book published, that can take a long time and involve many rejections before finally achieving a level of success. It's a better idea to take a position that allows you to write a book on the side, at least until you are established. The Kerouac model of bumming around as a struggling writer until you land a book contract is idyllic but more likely to end up in frustration. At least if you are working as a journalist, whether for a newspaper, magazine or website, you can pay the bills while working on your book.