Prelims is a screening test: General Studies Paper I (merit) plus CSAT Paper II (qualifying). Preparation is MCQ practice, PYQs, accuracy, CSAT on a fixed slot, and full-length simulations. Sample paper: Free GS1 Prelims mock.

Mains is the rank-deciding written exam: Essay, four GS papers, two Optional papers, plus qualifying languages. Preparation is answer structure, evaluated copies, Optional, Ethics and Essay — not more MCQs.

Official pattern: UPSC exam structure and syllabus. FIRST IAS does not treat Mains as “after Prelims only”: the methodology runs weekly Prelims + Mains mocks together, with writing checked daily. Also Prelims institute page and Mains answer writing.