To effectively critique practice answers for the UPSC Mains, focus on several key aspects. First, assess the clarity of the argument and whether it addresses the question comprehensively. Check for logical coherence and adequate structure, ensuring each point flows and reinforces the central thesis. Highlight any use of relevant quotes, data, or examples that support the argument. Additionally, evaluate the language and presentation, ensuring it is concise and formal. Finally, provide constructive feedback to help the writer identify areas for improvement, such as argument depth or analytical skills.