Scholarly articles of empirical research will contains sections on "Methods" and "Data" that describe how the research was conducted. As you develop your own research projects, you may need more information about the details of social science methodology.
Some Oxford Handbooks are entirely about methods, such as the following:
Other Oxford Handbooks focus on a substantive topic, but have chapters on related methods, such as the following:
The library catalog can identify other useful books on research methods with the subjects listed below:
These series from Sage, "Quantitative Applications in the Social Sciences" (little and green) and "Qualitative Research Methods" (little and blue) are concise, standard guides to specific methodologies. They can be identified in CBBCat, the library catalog, using the links below:
Some Oxford Bibliographies on Political Science, International Relations, and International Law focus on specific methodologies, with annotated lists of introductory texts, notable examples, data sources, and critiques.
Doing Feminist Research in Political and Social Science by 
Interview Research in Political Science by 
Case Study Research by 
Process Tracing by 
The SAGE Handbook of Social Media Research Methods by 