Get a comprehensive high school education. Music both influences and is influenced by other fields of study: the humanities, mathematics, the sciences, the social sciences, and the other arts-architecture, dance, film, literature, theatre, and the visual arts. For entrance into college-level study, you are encouraged to gain a basic overview of ancient and modern history, the basic thought processes and procedures of math and science, and familiarity with works in as many of the other arts disciplines as possible. Most professionals who work with music comprehensively develop a particular sensibility about the connections among music, history, and the other arts. Understanding the basics of math and the sciences support future work in music technologies. Social studies are related to understanding the context for various musical endeavors.
Think of everything you study as helping you become a better musician. As we have already said, the best musicians continue to learn throughout their lives. They are always studying and thinking, always connecting what they know about music with their knowledge of other fields. Since you never know the direction your career will take, it is wise to spend your high school years gaining the basic ability to understand and work in a variety of fields beyond music. Keep music at the center of your efforts, but accept and enjoy the challenge of gaining the kind of knowledge and skills in other areas that will support both formal studies at the college level and your music career beyond.
Source: National Association of Schools of Music FAQ page at http://nasm.arts-accredit.org/index.jsp?page=FAQ%2017