Common mistakes to avoid during UPSC preparation include neglecting the syllabus or focusing on non-relevant topics. Many candidates often underestimate the importance of current affairs, which is critical for both Prelims and Mains. Insufficient answer writing practice can lead to poor performance, especially in the Mains exam, where presentation matters. Additionally, time mismanagement can result in incomplete papers. Lastly, skipping revision can hinder recall during exams. Candidates must stay organized and maintain a disciplined study schedule to avoid these pitfalls.