If your school has a yearbook staff, join them. Bring your camera with you everywhere and take pics. Look at the websites of working photographers and see what are considered good photographs. How do your images measure up? Shoot what interests you visually. Look at the work of other photographers; why does an image attract you?
I have been a professional photographer for over 50 years and I'm still practicing and learning. Good luck!
Carrie recommends the following next steps: