What are the x(3) things I want to know about the candidate that I’m unlikely to find out even after I ask all the questions. Two important rules here:
These things should be relevant. For example, that the candidate plays ice-hockey does not really help sell him/her to me.
The candidate should not bother about his/her experience with technical tools relevant to the job: anything of relevance in this area would be covered via my usual line of questioning.
Do not make the interview an excercise in “Guess what I’m thinking.”
Apart from evaluating the hard technical skills (which is close to inaccurate), focus on the softer skills—juggling priorities, analysing requirements, writing technical documentation.
Ask about things the candidate is good at
So if he/she claimed (on CV) that they drove the adoption of .NET, focus on the drove, ask them to elucidate.
Ask about projects they worked on, whether they worked in a team or alone, how did they influence the direction of the project (if at all), toughest challenge, easiest thing to do.