Essential tips for mastering the UPSC interview stage include thorough preparation on current affairs and understanding government policies. Candidates should practice articulating their thoughts clearly, focusing on concise and logical responses. Engaging in mock interviews can help simulate the pressure of the actual interview, allowing candidates to refine their answers. Active listening during the interview is crucial as it helps candidates respond effectively to follow-up questions. Developing confidence and a positive demeanor also plays a vital role in making a favorable impression.