Hi,
First & foremost thing is building a rapo with the candidate & make him/her feel comfortable to speak out cause unless he speaks out we may not be in a position to judge the candidate.
Start talking to him , beginning from his family background i.e being more generic & later on his education background & slowly to his career profile.Ask him to talk more about his Company. Make him talk as much as u can & be a good listener. If he is a techie guy ask him more on his projects done show the curiousness to know more...
You should also have a candidate assessment form designed where everything gets documented.Eg. Communication skills, Initiative, Confidence level etc...
Thanks
MTS
This would be more applicable for junior & mid level candidates