This is a great question. I strongly recommend you either find an internship or start reaching out to people and look for a marketing mentor. There are so many different jobs you can have in marketing and now is the time to start exploring the industry, making connections, and speaking to people about what sort of experience you should get before you finish. This can also set the foundation for what internships you seek when you're about to graduate and can cue you up for a future job.
I also recommend reading/watching all you can online about different marketing jobs, different industries, and different cities that specialize in marketing. This will help you get a feel for where the industry is current at and will help you better plan your future as you decide on classes, internships, and future careers.
Lastly, I recommend checking out people's LinkedIn that you look up to. For example, I really am fascinated by John Wexler's carer path so I made sure to look at his LinkedIn and study his career path so that I can also mirror the things he has done that got him to where he is at.
I hope that's helpful and good luck!
1. Read marketing books to gain basic concept of marketing. You can probably look up books by Philip Kotler. He is known as the Father of Marketing.
2. Attend online marketing courses. Nowadays, Digital Marketing is quite hot. This may be something to explore.
3. Speak to your seniors that are studying Marketing in the University to get their views on what is Marketing and what do they like about the subject.
4. I am not sure if you are of age to work during your school breaks. If yes, you may wish to consider taking a part-time job in retail or online sales platforms to get first hand experience in sales or marketing, and understand consumer behaviour.
All the best!