Can They Think on Their Feet?
If you want to quickly determine how fast a prospective employee can think on their feet, introduce a brand new line of questioning out of nowhere. For instance, if the interview has been proceeding along a line of questions about school or work experience, from out of nowhere ask a question having to do with personal issues like hobbies or greatest childhood memories or what's their favorite movie. That moment in which you change the gears of the interview can provide a glimpse into how easily the applicant's mind can transition between unrelated subjects.
Interview Them All
Seems like a no-brainer, right? You've set up a series of interviews with prospective employees all week only to have someone who seems absolutely perfect for the job show up on day one. Do you hire him right then and there and make the phone calls politely informing all the others that the position has been filled? That would be the easiest thing to do. After all, time that you see being wasted conducting pointless interviews could be much more effectively spent doing just about anything else, right? Wrong. That shiny diamond who showed up on the first day may also have a series of interviews lined up and he may decide to go ahead and show up for his Wednesday appointment even after taking the job Tuesday. And that interview may have gone even better. Then there's always the possibility that the candidate you thought was a 10 on Monday turns out only to have been a 9.8 in comparison to the candidate who shows up on Friday. Not to mention the fact that everyone deserves an equal shot.
Be Charlie Rose, not Johnny Carson
You want to make the prospective interviewee as comfortable as he should be, but don't turn the interview into a talk show with you as the host. You are neither required nor expected by the applicant to make jokes or small talk. You are most definitely not expected by your bosses to start swapping stories and anecdotes. Keep it loose, but professional and try with all your might to keep the ratio of words exchanged to around 75% to 25% with your prospective employee getting in the lion's share.
Avoid Asking Anything That Can be Answered Yes or No
Unless you are asking very specific questions about very specific subjects that you absolutely need a one-word answer to, cross off all inquiries to which the applicant could do so. Most of those yes/no questions you might have in mind are probably either illegal to ask or can be answered by references, resumes or social media research. The only way to effectively gather the information you really need that cannot be procured through those other avenues--which, remember, is to find out of this person is going to be a good fit for your business--is to ask open-ended questions that has the potential to reveal far more than one-hundred yes or no questions.