Common mistakes candidates make during the UPSC interview include inadequate preparation, lacking awareness of current affairs, and poor communication skills. Many fall into the trap of overconfidence, leading to shallow answers. Insufficient attention to body language and formal attire can detract from their overall presentation. Additionally, failing to articulate personal motivations for choosing civil services may raise concerns among the panel. Effective preparation, including mock interviews, can help candidates avoid these pitfalls and present themselves more confidently.