To ensure effective retention of complex topics covered in the UPSC syllabus, candidates should adopt practices such as spaced repetition and active engagement. Creating summaries and concept maps can help break down dense information into manageable chunks. Regular review sessions, spaced over time, allow for reinforcement of memory. Implementing varied study methods, incorporating video lectures, discussions, and practice tests, can cater to different learning styles, aiding retention. Teaching concepts to peers can also reinforce understanding and retention. Lastly, maintaining a healthy lifestyle with adequate sleep and nutrition supports cognitive functions enhancing memory.