Strategies to enhance retention of complex topics for UPSC include creating concise summaries, using mnemonic devices, and teaching concepts to peers. Visual aids, such as mind maps and diagrams, simplify large volumes of information. Regular revision sessions are essential, utilizing spaced repetition techniques to reinforce memory. Engaging with interactive materials, such as quizzes or flashcards, enhances active learning and makes retention more effective. Lastly, connecting new information to existing knowledge helps solidify understanding and boost long-term retention of challenging concepts.