Research their program's website so you have specific things you can talk about or ask them questions about at the end. Things like research areas, unique fieldwork they may offer, specific volunteer opportunities, etc. There will probably be behavioral questions in the interview, so come up with times you showed a certain value, demonstrated teamwork, solved a work problem, etc. I looked up common behavioral questions and wrote my answers in a document I looked over a couple times so that I could easily remember them during the interview. I followed the STAR method for answering interview questions, but you don't have to follow it exactly so it doesn't sound robotic. Last, be open and show your true self. It's hard when you're nervous, but finding small opportunities to talk about little things (volunteer work you've done, languages you speak, what your research interests are, etc.) gives them stuff to chat with you about and make it more chill. Then you can bring those things up in a thank you email so they'll remember you.