Know your application inside and out.
If you have any low grades/test scores/GPA, be prepared to explain it thoroughly. During my interview, it felt like the basis was how I will succeed their super rigorous, hardcore, pain in the butt program that no other school will offer, if I have such low scores. Not sure about other applicants, but the interview felt more like an interrogation than an interview, but I hope it will be better for you (left a bitter taste in my mouth..).
As Cardsfan92 stated, look in the interview feedback section for NYCPM and look over the questions they asked students. Also, do a little research about the school, so you know what they offer and whatnot.
There will also be an interview with a student, but that one is more informal/relaxed.