Behavioral interviewing takes preparation and organization. Being prepared will make the interview go smoothly and get you the information you need -- fail, and you'll end up with an interview that is biased and ineffective. The first thing you must be aware of is to avoid your 'gut feeling' - intuition and instinct have a powerful place in the business world, but behavioral interviewing is a strict science. Applicants come into an interview determined to project the most positive image they can regardless of their actual skills and abilities -- and some people are simply gifted with the ability to 'sell you' on that image. The existence of these natural salesmen make the science of behavioral interviewing a very important discipline to maintain.
The first goal should always be to develop a set of bias-neutral questions that will determine if the candidate has the knowledge, skills, and abilities to complete the job. The best predictor of future behavior being past behavior, these questions should focus on relevant experiences from the applicant's history. Focus on open-ended questions that encourage reflection, long answers, and details. Make a list of such questions.
When the interview actually starts, stick to your script. No matter how interesting or intriguing a story is, don't allow the applicant to derail the focus of the interview. Remember the amount of preparation you put into this interview, and don't let it go to waste by improvising or wandering off-script.
Give the applicant plenty of time to answer these questions -- don't feel the need to fill any long silences; allow them space to think. When they do answer, take lots of notes. Not only will that force your focus onto the salient details, but it will help you remember your instantaneous responses to the answers given when the time comes to review the applications later on. Fail to take notes, and you run the risk of relying on your intuition rather than an accurate memory of the answers given.
Keep strictly to this careful behavioral interviewing process, and your chances of hiring top performers expand exponentially.