The ratio of opportunities to Candidates invited for interviews for PSUs usually range from 1:6 to 1:10. Your GATE score remains the most important factor to be shortlisted for an interview. There will be atleast 7-9 people in the Interview Panel. So you have to prepare for any sort of question that is asked of you. This comes with practise and so Mock Interviews will help you build your confidence, help you build your technical knowledge and also see where you are among your peers. Infact, that is a good idea to attend Mock Interviews. You can get a hang of what you may have to face on the D-day. Also keep yourself updated with the current affaris, know a lot about the organisation that you have applied for Interview. Most Companies ask  questions like "Tell us about yourself", "What do you know about our Company", "Why our Company", etc. Try to keep yourself informed about the important aspects of the Company you are planning on attending interview for. Few questions will be also regarding the Project you have completed during your Graduation. So be specific about that too. If you are not someone who can initiate a group discussion, when given a chance to speak, be clear about your thoughts and also listen attentively of what others have to speak. Think before you speak and listen while others are speaking. Also you are not expected to know the answer to all questions. So it is ok to accept if you do not know the answer to any question. Try to implement these even in the Mock Interviews and check your performance and ask for feedback if possible. This should keep you ahead of others. Good luck:)