Reliable sources for UPSC exam preparation typically include standard textbooks recommended by experts, NCERT books, and government publications. Reputable online platforms that offer coaching and curated study materials are also considered trustworthy. Following leading newspapers and reputable magazines for current affairs ensures authentic information. Previous years' question papers and mock tests from established coaching institutes provide practice and insights into exam patterns. Additionally, guidance from experienced mentors and forums where aspirants share resources can serve as valuable tools for efficient preparation.