It is actually easier than you might think... but you have to pay attention to very subtle things and what people actually say. Probably the most prevalent error interviewers make is to "hear" a person say what the interviewer wants them to say rather than what they actually said.
I start with pretty simple questions then target things in their answers for follow up.
"Why do you want this job?"
"Describe someone you felt you worked well with"
"Tell me about a time you had conflict with someone at work and how you handled it".
"Tell me what you think makes a good supervisor... someone you enjoy working for" (If they say someone who pats them on the back alot then that's a concern since they may be "needy". I need folks who find satisfaction in doing the right thing)
Basically, I ask starter questions like these... then start picking the answers apart by asking more questions... sorta like I do you guys here sometimes except it doesn't come off antagonistic in person. I want to know things that the applicant did not come to the interview to tell me about how they relate to other people and their attitude about work.
Most companies do not hire that well. I've worked for a few companies now. Oddly enough, most companies spend little time training their managers to interview and hire. It took me time to really start noticing the important things. It is similar to knowing how to "do" college. What's important? What's not? What do you study multiple times? What do you glance over?