I got 5 interviews so far; I would recommend, try to be relax as much as possible. The tension you may have may significantly affect your conversation with him/her. If you are really stressed out like me, I'd recommend a shot of whiskey
Try to be yourself, I am sure you are going to reply them since they have seen such a spark in you, they wanted to make an interview.
I am not sure how things are going on in Psyc/Human Dev interviews, but i believe they are almost same in base. Instead of testing my skills or abilities, most of the time they asked me what did I do and what I want to do, what's my research interest.
And always smile during the interview whether the video is on or not. They sense that!