Obtain an internship at a recording studio. There you will receive valuable hands-on audio recording training and will have the opportunity to network with many experienced engineers and musicians.
Take as many music and audio courses as you possibly can. Music theory courses will help you understand the many components of musical and harmonic construction. You will also learn how to listen to music with a critical ear, which is an essential skill for the mastering engineer.
Make a checklist of the equipment and space you need. A very basic mastering studio will consist of a high-speed computer, professional audio mastering software, mixing hardware and a high-quality pair of speakers for mixing and mastering. You do not need much space, but you will need a comfortable space where you don't mind spending countless hours mastering audio tracks.
Hire an acoustic technician to properly sound-proof and tune your work room. It is absolutely essential to have the most neutral-sounding room possible when mastering music. The shape and size of your room has a direct effect on how music will sound in your workspace. This requires the expertise of a well-seasoned acoustic technician to properly design the layout of your room.
Create a website for your business. Your website should provide background information about your recording experience, your mastering studio and a method for delivering the audio files for mastering. Be clear on what types of audio files you accept from clients.
Promote yourself. Start a Myspace and Facebook page for your mastering studio. Advertise on Craigslist and consider starting a Twitter account to keep potential clients constantly updated on your business. Don't underestimate the power of social networking.