Gain undergraduate and postgraduate qualifications. These are required before you can study a PhD. Try to gain additional voluntary work or academic experience during study for your undergraduate and master's degrees. Taking elective classes or getting a voluntary job in the field of music can help you stay ahead of the curve; teaching experience is important if teaching music is your ultimate goal, since many music historians end up working as teachers.
Take classes in related fields. Both the University of Chicago and University of Toronto require you to take several supporting courses whilst pursuing your PhD. These classes can be in various fields, including tonal analysis, enthnomusicology or other forms of musical analysis. You also need to take one course in music before 1600 and one course in music after 1600 while pursuing your PhD.
Learn German, French and Italian. Music history PhDs require knowledge of at least one language beyond English, and many have language examinations that must be sat by students. German, French and Italian are the most commonly requested languages, but Latin would also be beneficial. Taking time to learn these languages can help you pass through the examinations and gain your PhD.
Learn about musical traditions from the ninth to the twentieth century. To gain a PhD in music history from the University of Chicago, for instance, you have to have a virtually encyclopedic knowledge of different musical movements throughout history and the history of European musical traditions. On some courses, you are tested on your ability to identify scores or excerpts from between the ninth and twentieth centuries. You are also required to conduct one in-depth tonal or atonal analysis.
Work on musicianship skills. Learn how to sight-read, sight-sing and musically dictate. Schools such as the University of Chicago require PhD students to sit several musicianship exams during their residency, and these focus on the skills listed above. The University of Chicago also requires that students play in a musical ensemble for over a year concluding with one public performance.