So, let's start with the basics. Interviews are not an exact science. They are not meant to be. The best you can do is to try and remove as much of the emotion of the process as possible and balance it with logic.
Interviews should be about helping candidates show their best side, it is not about tricking them, putting them under added stress and seeing how they "perform". They are not seals; they are human beings complete with human feelings. Interviews are of themselves inherently stressful - so even in the most relaxed interview you are getting a person operating under stress.
Here are some tips to help you with your job interviews
Before the interview:
1) Make time in your diary for the interview. You need to show candidates the courtesy of being fully "present" at the interview. If you need to, hire additional staff to cover for you or close the shop for an hour.
2) Make sure there will be no interruptions. If you allow yourself to be interrupted during the interview you are giving candidates the message that when they work for you they are unimportant and will always be second best. Is that the message you really want to give?
3) Work out exactly what you are looking for. Of course you have a position description for the role written. If you don't, you need to write one before the interviews so that candidates know exactly what the role will entail. Once you know precisely what they will be doing, work out what skills and experience are essential in order to be able to perform the role.
4) Work out the sort of person you need for your team. Fitting a person into a team is a real jigsaw. If you are a scattered sort of person, perhaps you need to look for someone organized to balance your gaps. It is easy to get carried away with someone who is a nice person, but if they don't have the skills or the right personality for the team then they are the wrong person for this role.
5) Make sure you are not directly or indirectly discriminating. Do you really need a "bloke" for the role if it involves heavy work? Gender is not a good predictor of strength. Some of the weediest people I have met have been blokes and the strongest people who can bench-press better than everyone in the gym are women.
6) Contact the candidates. Let them know who will be interviewing them, how long they can expect the interview to last, where to come and where they can park. By showing them courtesy as if they are your top client, you are sending a very strong message about what it will be like to work with you.
7) Somewhere to wait. Make sure there is somewhere nice to wait before the interview. Some candidates can arrive up to half an hour early, so be prepared.
8) Work out the questions you are going to ask. These questions should be directly linked back to the duties of the position. You need to ask each candidate the same basic set of questions so you can compare answers. Of course you can prompt for more information, but the basic questions should be the same. Also work out the sort of answers you would expect to see from a great candidate.
9) Check your questions actually give you the information you need. If you ask "can you use Microsoft Word" you will get a Yes/No response. If you ask "tell me how you would go about setting up a mail merge letter to my database" and you get a better idea of their skill level.
10) Consider giving candidates the core questions 15 minutes before they come in for interview. Remember you want them to be the best they can be. In most jobs people don't have to answer off the top of their heads all day every day. People have time to think. By allowing people the chance to see and think about the main questions before the interview, you allow introverted people the chance to shine. Interviews traditionally favour extroverted people, which means that you are missing out on at least half of the population.
11) Consider having more than one person in the interview. Different people see different things in candidates. It can help to balance out viewpoints.
During the interview:
1) Introduce yourself and take some time to build rapport before launching into questions.
2) Allow the candidate space to be nervous. Make sure they have a glass of water to drink to steady their nerves.
3) If conducting a phone interview, periodically make some noise when they are talking such as "aha" or "mmnn". Phone interviews can be disconcerting as often all the candidate hears is silence. Consciously fill the background and you will get a better interview.
4) Check the referees are still current (you may want to ask the candidate what they think the referees will say about them - always enlightening).
5) Remember the no interruptions rule. Once you are interviewing allow no phone calls or people barging in. If someone does barge in, apologise first to the person you are interviewing. Tell the person who barged in that you are interviewing at present and will get back to them in half an hour.
6) Ask if they have any questions for you and be prepared for any curly question about you, your company, pay and conditions, development opportunities and promotional possibilities.
After the interview:
1) Check references of all candidates you are seriously considering.
2) Personally ring every candidate you interviewed to tell them they have been successful or unsuccessful. Give some basic feedback on how great they were at interview but the field was very competitive.
3) Follow it up with a short note thanking them for their time and interest in your company and wishing them well for future roles. It costs nothing for courtesy but builds a great image of you and your company.
When all is said and done, you need to balance logic with gut feel about the candidate. If your gut says no but they are a great candidate, check it out further with more questions or reference checks. Your gut usually has picked up something that you need to know more about, so trust its wisdom and dig a bit deeper.