Whether performing or teaching, a successful musician needs a background in several musical instruments. Theory and composition classes are almost impossible without some basic skills in piano or keyboards, and school music teachers need some basic knowledge of band and orchestra instruments. Even rock musicians need some skills in guitar, bass, keyboards and drums to get along.
Although a college degree may not be necessary, a few courses in music theory are well worth the effort. Music has its own written notation and spoken language that has developed over the centuries and is known to musicians throughout the world. A knowledge of intervals, key signatures, chord theory, timing, sight reading and composition allows you to communicate your ideas to others and will enhance your skills.
To become a successful musician, the most important factor is practice and repetition. Unfortunately, many musicians spend their time practicing their mistakes. A cheap digital recorder allows instant feedback that highlights mistakes, inconsistent tone, irregular timing and other problems. Recording, mixing and production are also valuable skills in their own right. Anyone with a computer, some open source software and a few extra dollars can put together a near-professional quality recording studio and begin creating great music and gain valuable experience.
In addition to practice, another important skill is performing. It takes a lot of courage to get up in front of other people and make music. Find a place where you can get together with other musicians to perform: open mike night, church service, school choir, community orchestra, jam sessions.
There are a wealth of jobs in music education, and gaining the skills to teach is as close as the nearest community college. These courses provide the basics in communication skills, teaching methods, how people learn and how to build a training plan. There are always jobs available in public schools and colleges, or even teaching kids how to play the piano.
Besides music, a professional musician or teacher needs to have basic business skills. A few courses in small business, organizational behavior, finance or business law will help when it comes time to negotiate a contract, file a copyright, register a small business license or just balance the checkbook and pay the bills.