Common mistakes candidates make while preparing for the UPSC exam include inadequate time management, focusing excessively on non-essential topics, and neglecting revision. Many aspirants struggle to balance the vast syllabus and fail to allocate time effectively across various subjects. Additionally, relying heavily on a singular resource or method can limit understanding, while ignoring multiple perspectives and sources can lead to gaps in knowledge. Lastly, some candidates may underestimate the importance of current affairs and neglect this component until later stages, which can significantly impact overall performance in the examination.