Honestly, just be open-minded to the experience. Know that you are going to experience a world very different than your own, and that is something beautiful. Not knowing what IVHQ, India, volunteering in a third world country, or international flying was like was scary, but amazing. I'm glad I had no idea what to expect. Granted, I still did lots of research, read reviews, articles, and the booklet in order to learn about India.
The only thing I can think of that I wish I had known ahead of time was how much free time there was. I did not realize how much I would want to travel outside of the placement. I only went to a few cities near Delhi, but wish I had gone to more.
If you are thinking about going overseas, you have already taken the first step: considering something outside of your comfort zone. You might have already started dreaming up places to go. Go! This trip helped me see/learn things I would never have before. And it made me realize that traveling is possible for me.