Common mistakes candidates make while preparing for UPSC include neglecting current affairs, inadequate time management, and lack of clarity over the syllabus. Over-reliance on one source of information can lead to knowledge gaps. Additionally, many aspirants underestimate the importance of answer writing practice and fail to develop a structured approach. Another mistake is not revising regularly, which can result in forgetting previously studied material. Recognizing these pitfalls can help candidates adopt more effective strategies, increasing their chances for success in the exam.