Key aspects of the Indian Constitution important for UPSC candidates include the Preamble, fundamental rights, and duties, as well as the Basic Structure Doctrine. Candidates should also focus on the distribution of powers between the Centre and States, various provisions related to governance, and recent amendments. Furthermore, knowledge of landmark Supreme Court judgments and their implications on constitutional law is crucial. Understanding the Constitutional Framework aids in tackling both Preliminary and Mains exams effectively, as it forms the basis of many governance-related questions.