There used to be a time when people could apply for jobs in the publishing world and have a couple of offers to chose from. Today, life isn't that awesome. (If only, right?) It's pretty difficult to land your dream job, no matter what profession your in. But if you're looking to get a job within publishing it's best to start early.
After graduating from my university and working a corporate job I hated, I decided to go after one of my passions: books. I wanted to work in an industry that was surrounded by books because as a writer, I also love reading.
My advice to you: If you KNOW you want to work in publishing, fashion, music--whatever--you should start early. Although most companies won't hire people without a degree, you should always be open minded to internships while attending school. EVEN IF IT'S UNPAID (Which most of them are.) Yes, I know it may suck. But you know what? YOU'RE GAINING EXPERIENCE. And EXPERIENCE is what the little resume people look for when scanning through your resume and portfolio.
If you're only in high school? Who cares! I know a ton of high schoolers who are interning for authors, publishers, and literary agents. Let's face it, you know they're busy! Even if you're just going through their email, queries, files, grabbing coffee--you're still DOING something. You're still immersed in the atmosphere and getting a taste for the job you actually want. Don't let your age set you back!
Where can I find these magical internships, you ask? When I interned for Folio, I actually found the intern position at bookjobs.com. Not only does this website list publishing job openings from the Top Six publishers, it also lists openings from some boutique agencies. Take your pick!
Let me warn you (and this is my biggest pet peeve EVER) you'll have to apply to more than FIVE jobs/internships if you're looking for a reply. I applied to over 150 internships before I got mine. I'm not even joking. I can totally screen shot my sent box if you don't believe me. But let me just say this too, IT DOESN'T MATTER what dream job you want, 95% of the time you will have to go above and beyond and apply the heck out of places before you get an interview. So don't hold back! And don't give up after like, 5 applications.
There's a lot of other awesome publishing websites that offer job openings, too. Remember to be persistent and don't give up on something if you really want it! :)