Anything I Should Do?

Hi, I'm a high school junior who is interested in a career as a copywriter. I have a passion for writing and it's very rare for me not to write at least something every day. Now, I was wondering if there's anything I should do right now as a high school student to gain more experience as a potential copywriter - just to grasp what it is like as much as possible? I have thought of interning for advertising companies that are around but I have no idea what to say or how should I go about making a resume due to my little experience with advertising.

I'm a copywriter and I wish, more than two decades ago, I had your prescience. I'd be retired now and I'm in my 40s. Seriously. Here's my advice.
Dan Kennedy wrote his first sales letter when he was 17. Write a sales letter for you--if you offer a service--or help a friend who offers a service--like lawn care. Simple letters sent around the neighborhood can be extremely powerful.
READ...there's no need to purchase all the expensive manuals, etc. You'll find all the information you'll ever need about copywriting in books and in blogs. Start with this book: Scientific Advertising. It's free on Michael Fortin's blog. Read books by Herschell Gordon Lewis, Dan Kennedy, David Ogilvy, Andrew Wood, and Bob Bly. Ogilvy is dead so he doesn't have a blog but the others do.
CHOOSE YOUR NEXT STEP CAREFULLY...you're looking at colleges. I don't think there's a college that offers a degree in direct response copywriting but find one with a good English department (writing) and a good marketing department. Take psychology courses.
SET UP YOUR OWN SITE AND START SELLING...Very quickly, you will learn how to market.
UNDERSTAND THE TECHNOLOGY...extremely important.
READ SOME MORE...read writers like Hemingway who could say a lot with very few words.
LEARN TO SELL...Get a job in a store. Tell the owner/manager you want to learn how to sell. Choose a store with a sales culture. Read books about selling. Learn A v. B and other closing techniques. The store owner will not want you to leave.
WRITE A BOOK...it's the best way to learn. Write it during college. When you interview for jobs, you will be the ONLY college grad to have written a book about copywriting.
BUILD A PORTFOLIO with actual results.
BE A DIRECT RESPONSE COPYWRITER...I'm biased but branding advertising is fluff. It's the top direct response copywriters who are the rock stars.
If I can help you some more, let me know.
I love writing (17 books, thousands of articles) but direct response copywriting is best.

Oh wow, thanks so much for the advice!
I have already started trying to set up my own site so I will definitely put more effort into that as well as everything else.