- Some schools offer AP Psychology for juniors and seniors. I remember this being an incredibly competitive course to get into because EVERYONE wanted to do it.
- Sociology if your school offers it. It'll give you some insight into social psychology
- Anatomy. Having a foundational knowledge of the brain, body, and neurotransmitters can be helpful
- AP Stats. As a psych major, I took at least 4 stats classes over the years. It's a large component of psych, especially research! It's okay if you don't completely understand it the first time, I sure didn't. but it will give you a preview of what's to come
- Volunteering at a non-profit. It doesn't necessarily matter where as long as you're passionate about it. It will give you experience on how to work with different kinds of people
- Tons of high schools offer free or reduced-cost access to community college courses. I remember taking a psychology course during the summer of my senior year which gave me a leg up when I got to college.
Some things you can do in high school is volunteer at shelters or other human services locations. You can volunteer in a hospital setting if you would like, though you may see a different severity of conditions in hospital settings. You can see if your school offers any dual credit Psychology classes or if you can try a Psychology class at community college. You can also search videos online and talk to mental health professionals here or in person. You can also browse college psychology classes and see if they sound interesting to you. You can also talk to your school counselor/advisor--I believe they should all have a psychology and helping fields background. Good luck!
Psychology is a great field! I would recommend getting some shadowing hours. When you start shadowing a Psychologist/Psychiatrist, you get to see how they interact with their patients, how they get to their diagnoses, etc... This will really help you understand if you want to be in that field or not. When you get to college, its best to take psychology courses, even if you don't major in Psychology, just to get the core classes and have a better understanding of the field. As Jackson stated, getting a part-time job or becoming an intern would really help you get the experience you need as well.