Candidates must master principal themes in the Indian Constitution for UPSC, including Fundamental Rights, Duties, the Directive Principles of State Policy, and the structure of the government. Understanding the separation of powers, checks and balances among the executive, legislative, and judiciary, is crucial. Additionally, knowledge of amendments, important cases, and notable articles helps in answering both MCQs and descriptive questions effectively. Clarity on these themes aids candidates in relating constitutional concepts to contemporary issues, enhancing their analytical abilities.