IT professionals often wonder what level of technical preparation is required for an interview. From my experience conducting interviews, I can say that people are generally asked interview questions based on things they have mentioned in their resume.
People often fail in interviews just for one reason -- i.e., they mentioned too many things in the resume and they were not prepared to discuss them in the interview. Of course, mentioning a lot of things in your resume which you have not worked on, can also be a big issue!
So, the basic criteria is to prepare yourself by reviewing everything you have mentioned in your resume, and your success rate will be above 60%!