Indicators of a well-prepared candidate for the UPSC Mains include a comprehensive understanding of the syllabus and strong analytical skills. Candidates should be able to express their thoughts coherently and demonstrate an ability to integrate knowledge from various subjects. Regular practice with previous year papers and mock tests is essential for improving time management and writing skills. Additionally, awareness of current affairs and the ability to critically analyze issues are key. Overall, a combination of content mastery and effective communication skills characterizes a prepared candidate.