Hi,
The best suggestion I can give is to prepare well. I thought that was just a casual talk (perhaps it was for the DGS), but English is not my native language, plus I was nervous and poorly prepared to answer questions, all of these made a huge difference to my performance. So no matter how ‘casual’ it looks like, prepare for it like you’re attending an important interview.
Also, if you’re using Skype, remember to make eye contacts by looking into the camera, not the screen, for obvious reasons.
He asked four questions:
1. What’s your biggest concern about the program?
2. There will be TA jobs as well as coursework, how will you manage the heavy workloads?
3. Tell me about a class discussion that you’ve had. (I’m pretty sure I screwed up this question)
4. What other schools are you applying to?
I’m an international student applying to master’s programs, if that helps clarify things. Good luck!