please help with interview preparation questions

I'm preparing interview questions for .net positions. I read a lot online questions but when it comes to technical interviews, I feel my skill couldn't cover all questions. Honestly, I always missed a few. My question is how good I need to answer the questions. When you miss a few, Do the interviewer think you are done in general? If a question you are not quite know, what's the best way to handle it and continue interviewing? Thanks!