You have to be inquisitive, curious, self-motivated. You have to be energetic and willing to be wrong, as well as right. But if you have passion for your subject matter, and determination, you can succeed as a scientist. Study hard, etc. But also you can volunteer.
Many organizations offer volunteer opportunities for high school and especially college students.
You can also get internships. These will provide valuable experience in the real world as well as job contacts. This will provide you with much needed experience, job contacts and help you decide of the career is right for you. Again, take lots of science, study hard and be involved in a variety of activities. Try to visit other institutions.