One-word advice I could give to a new high school students is : RESEARCH!!
I could not imagine my life without any research experience. All the research programs I have been involved in, especially SROP, have really opened a lot of doors for me. I have been able to develop personally and academically by doing research. Programs like SROP, which is a rigorous program develops your communications skills, analytical thinking, preparedness for your future is a great experience. Personally, SROP has exposed me to a new environment I have never experienced. All the workshops, and interactions with diverse students opened my mind to new ideas and awareness. SROP has also been an educational and learning space where I have learned about other fields, which makes me more competent.
Thus, I would tell a high school students to go FOR IT!! Research will prepare you for the work in the classroom. It will help you develop your writing skills, your responsibility and determination as a student. These skills will be developed while doing a research project, which will make it easy while doing class work. Also it will help you develop personally, because you will learn a lot about yourself, how you react when you are under pressure, how much you know about different diverse backgrounds.
Generally, research is a great experience because you learn about your field of study, and you develop personally and academically. You will not regret it! Plus, your research project could be anything you are passionate about. You can do your own research project, for most cases, unless you are more in STEM fields. But even then if you really are passionate about a topic you could make it work!!