Some would say, don't go into that job at all, because you literally NEVER get paid at all.
While that's almost completely true, ignore those people. Because, it's a legitimate career, and there are ways to make sure that you DO get paid.
My advice is, write at least 25 books, not just one. Not even five or ten. Write a minimum of 25 books.
Also, once you are already a published author, you could see if you can write for a newspaper (even though newspapers practically don't exist anymore). Find a newspaper that's online now, and not still in the traditional paper form. They might still be around for a while. Put "Published Author," and the year that your first book was published "to present" on your resume, if / when you do apply for that job.
Do book talks at book stores around the country.
Write about what you are passionate about, or anything that you have something to say about. That way, it will be easier to write the book, and the book will have substance, meat, and proper length, as well as a purpose.
Don't let one "no" from a publishing company stop you from writing. Keep trying until a publishing company says "yes." If ALL of them tell you no, that's why there's the option of self publishing. Once your book is successful enough, the publishing companies will see that they should have told you yes. Even if it's self published, you can still put on your resume that you are a published author.
Always copyright your work before submitting anything to anyone. That way, your work will truly be your, legally. If you don't, someone else will. Most likely publishing companies. If they don't, individual people will.
Write out how you want the book to go before writing the final version. You don't have to write the book repeatedly. Just an outline of what you want to do, or various notes, or topics in the book, or quotes you want to put in the book, or things like that.
That's some tips.