Qualifications
You'll need a BA degree in music education and a teaching credential to teach K-12 in public schools. Some private schools don't require credentials, but better to cast a wide net, right? If you want to teach at the collegiate level, you'll need at least a master's or maybe even a doctorate in music.
Salaries are often commensurate with education level, so get as advanced a degree as you can afford to keep your options open. The bigger the degree, the bigger the bucks.
Private schools vary, though all require a BA and many want to see a master's degree. Also, being really talented and being a studio musician on Beyoncé's last album can't hurt.