If you are a high schooler, I would recommend that you take science courses, especially AP science courses, such as biology, chemistry, physics, and psychology. These courses will help prepare you for the basic science courses you'll be taking in college. In fact, if you score well on the AP exams, your college or university may give you college credit and/or allow you to skip the first level of these courses, allowing you to move to more advanced courses earlier on. I would also highly suggest getting involved in the medical field to make sure that a career in medicine is really what you want to pursue. This can mean volunteering at a hospital or clinic, shadowing doctors, and/or doing research.
If you are in college, you don't need to be a science major to go to medical school, but you will need to complete the premed course requirements. You should meet with your academic advisor to make sure that you take all the necessary courses to apply to medical school; these will include biology, general chemistry, organic chemistry, physics, math and statistics, and humanities courses. You will also need to take the MCAT, which you can prepare for through your classes and by purchasing MCAT prep books from Kaplan and/or Princeton Review. I would also highly suggest continuing to get involved in the medical field to make sure that a career in medicine is really what you want to pursue. This can mean volunteering at a hospital or clinic, shadowing doctors, doing research, scribing, or working as an EMT.
Hope this helps, please let me know if you have additional questions!
Best of luck!