Consider these questions when formulating your research question:
This is the first place you should search when doing music research. Use it to find background information about your topic, and pay particular attention to the bibliographies at the end of each entry. They can provide you with great sources!
Sample searches:
Schubert AND "piano concerto" AND (analysis OR criticism OR interpretation)
Schubert AND (society OR culture OR politics OR philosophy)
"elizabethan melancholy"