Interviewing should be the most useful tool in the entire hiring process, assuming you know how to handle it. Statistically, it is one of the weakest indicators of success. I think much of the reason for that is a) the lack of skill/training and preparation of the people we choose to conduct the interviews and b) a fundamental weakness in knowing what skills you are looking for.  Approach each interview with a sense of purpose. Effective interviewing requires a systematic approach. The worst thing to do is approach the interview as if it were a conversation with the purpose of "just getting to know each other." 

Successful techniques:

GET CLEAR on your objective! Before reviewing a resume, before speaking to a candidate, get clear on your objective. Outline on paper the following: 

• What are you hiring for? 
• What do you need?
• What characteristics will have the most bearing on the candidate's ability to handle the job effectively?
• What specific tasks need to be performed? What values and personality characteristics will work best in your organization? 

PLAN, PLAN, PLAN the interview   --  When reviewing resumes, get conscious about the judgments you are making based  on the resume. An interview is about eliciting information NOT affirming judgments. What aspects of this person's background do you want to address? What qualities seem to jump out at you? Remember these qualities are your assumptions. Think about what questions you can ask to confirm them. Interviews are stressful, so start the interview by helping the candidate to relax. A welcoming approach and brief small talk will help establish rapport and ease tension. You elicit information from a candidate more effectively if you help them feel comfortable. Outline for the candidate what the interview is meant to accomplish. Do not  describe the job in detail. State why the candidate is interviewing and what kind of information you want from the candidate. ("We are interviewing for an Project Manager. What I want to learn today is how you believe your experience and personal strengths will make you effective in this position"). 

It is a tactical mistake to reveal details about the position early in the interview. Two reasons for this: 1) A shrewd candidate will interview in a way calculated to give the impression they match your criteria for the job.2) The more you talk, less time you have to elicit information from the candidate.

LISTEN! LISTEN! Let the candidate do the talking. Keep you're talking down to about 25 percent of the interview. Everything you say should be directed towards getting the candidate to talk. Experienced job seekers will do their best to get you to do the talking so they can assess how to answer your questions, or shift focus of conversation towards their strengths. Don't let the candidate control the interview! Jot down their questions and tell them you will answer them at the end of the interview. Stay focused on YOUR objective which is to elicit information. 

Take Notes. Most likely you will interview several candidates for one position. Consequently you're likely to forget details of your  interview with a particular candidate, and at evaluation time you're left with a "gut"  reaction. So take notes!

EVALUATE the interview. When the interview ends write a brief  evaluation of the candidate. What struck you as the candidate's strengths and weaknesses relative to the requirements of the position? Did you get sufficient coverage in terms of the candidates technical skills? Values? Personality? Review your performance during the interview. Did you obtain the information you needed? Did you listen enough? Did you stay in control? How might you adjust your technique next time? It happened (or will happen) sooner or later to all of us. We stopped interviewing to get hired and found ourselves interviewing candidates of our own, from the other side of the table.  It's not something that comes new with the new job. Those who did it will know it IS the job, or at least the single most important part.

Suggested Interview Questions:

• Who do you report to?
• What is your supervisors function ? (this question gets to what the candidates real work is)
• Describe your typical work day? (This question gives you idea how a candidate's duties relate to the job you're hiring for)
• Tell me about the people you hired in your last job.
• How many?
• How long did they stay?
• How did they work out? ( this question gives you idea of candidates ability to assemble and keep a strong staff)
• Describe what it takes for a person to be a successful [fill in job person is interviewing for]? (This question is  indirect way of having a candidate reveal their own strengths and weaknesses).
• What strengths did you bring to your last job that made you effective? (another indirect way of revealing strengths or weaknesses)
• How do you go about making important decisions? (This question gives a sense of how the candidate is likely to operate on the job)
• What are some things your company might have done to be more successful? (This question can give you evidence if the candidate gets the "big picture". If they can't answer this shows lack of depth. This question can also elicit negative feelings the candidate is harboring towards current employer. This could reveal personality problems).
• Why are you interested in this job? (This question separates the candidate who just wants any job from the candidate). 
  whose career ambitions are consistent with the job opportunity).
• Why have you decided to leave your present job? (This question can reveal what motivates a candidate: career  growth, money, personal challenge)
• What is your most significant accomplishments in your business life? (This question substantiates strength)
• What have been the biggest failures or frustrations in your business life? (This question often reflects self knowledge, and how comfortable they are revealing weaknesses).
• What risks did you take in your last job, and what was the result? (This question separates out average applicants from superstars. Studies show that highly successful people take calculated risks. Also gives insight into candidates judgment).
• Tell me about a failure in your life and why it occurred? (What your looking for here are signs the candidate is able to accept responsibility).
• When you have trouble solving a problem, what are you likely to do? (this question indicates how dependent or independent the candidate is likely to be)
• Describe the best boss you ever had. (This question indicates what kind of supervision the candidate likes)
• What differentiates you from other applicants? (Indicates how well the candidate understands the position.)