The Oscola Guide contains information (p. 37) how to cite Judgments of the European Court of Human Rights (which is missing in the Oscola Citing International Law Guide).
Step 1: Consult a textbook when you start with a specific topic that is still (partly) unknown to you.
Step 2: When reading textbooks etc. note down document references. A document reference is a good starting point to find literature.
Commentaries on different treaties are also very interesting sources for information, references etc.
Step 3: Journal articles will point to relevant sources law, key concepts and legal developments. These journal articles contain furthermore: book reviews, bibliographic information, reports of cases. Yearbooks are useful for orientation, quick reference and the development in a specific field of law.