The purpose of an interview is to assess the skills, experience, and cultural fit of your potential employee.
These articles will help you prepare to conduct an effective interview:
Interview Tips and Interview Techniques -- This page includes lots of great information and links on conducting the interviews including conducting powerful interviews, best practices for interviews and more.
The Interviewing Cheat Sheet: 100 Resources for Interviewers and Candidates
Pop Quiz: Will you be using Behavioural or Results oriented technique for your interviews and why? If you can't answer that question, go back and read the information over again.
Scheduling Your Interviews
Questions should take an average of about 1-2 minutes each but can be much more if you end up with a very verbose candidate. If you only have 10 questions, the interview could be as short as 10-20 minutes. If you aren't conducting in-person interviews, try to make the interview longer. If you run across candidates who are obviously overwhelmingly not qualified, feel free to cut the interview short and take a break.