The below are my interviewing principles aimed at intermediate-level people who conduct standalone job interviews.
The first interview I've ever conducted was at Palantir, 2.5 years ago (at the end of 2012). An interviewer dropped out and there were only the 15 of us in Europe at the time - so I had a whopping 10 minutes to prepare for an interview for a different role than mine. It was seemingly a disaster - the interviewee was several levels above me intellectually at the time and owned the interview. 140 interviews later, I don’t think that it was a disaster anymore (although naturally one of my weakest interviews). My goal was to find the truth about his technical abilities - and I accomplished just that. We hired him and now he’s one of the strongest execution people in the European business.
What follows is a set of interviewing principles which apply to all roles. The role-specific parts of interviewing are signal collection and the hiring decision and these are outside of the scope of this discussion.