Also, pick the right classes in school. Writing courses as messaging and writing are a critical skill for all marketers. Public speaking or debate are great as you need to be persuasive in Marketing. Also, lots of Math classes. Reporting and analytics are INCREDIBLY important in modern marketing organizations. Some creative/Art or design classes would also serve you well. Good luck!
If you have something that adds value to customers, either through making life easier or by adding enjoyment, then 90% of the work is done. At this point, it is about looking for your target or niche audience and understanding what we call their "love language" or their preferred method of communication. This takes practice amd lots of sitting back and observing amd going through data, so you must have patience. Good luck to you and remember, find something that you truly love to do, not just something you may be good at, and the support will come to you when you need it.
You are off to a great start! You're asking questions already! What kind of marketing person would you like to be? User Experience Optimizer/Analyst? Data researcher or content creator? The best way to prepare is to start reading. Read books and articles, watch YouTube videos and listen to podcasts. There is a ton of information out there these days. You can use your Facebook browsing time. For example, collect ideas for a blog and for your social media. Browse the latest web design trends.
You'll want to read about content marketing, email marketing, SEO marketing, digital marketing, B2B marketing, direct marketing, Social media marketing, etc. Do you like to write?
Hope this helps!