So in order to start writing books you don't need to join a career path, you can register as a self-employed writer though. First you'll need to start by 'Practice Writing' at the computer. After you start from here you'll get the option to 'Refine Writing' on the computer. The further along you are in the Writing Skill the larger the royalties, the more likely your books will be a hit and the more options of genres you have to compose.

I recommend starting to compose books after you've gained two or three skill levels. You don't need to worry about refining your Writing Skill after you start writing as, like most other Skills, it levels up as you use it.

Note: if you click on the Skill tab and go into the Skill window you can see what genres of books are giving the most royalties at the time.
There are also Lifetime Rewards that can help your Writing career. Example: Acclaimed Author.