Not to be difficult or anything, But I was applying for a position in Emergency triage, in a hospital with a rigorous volunteer program. The interview was over 45 minutes long and she asked me questions such as "what is your greatest weakness/strength" etc. I think prior to the interview she was not so hot on my application (no prior hospital exp), but based on my interview she was glad to give me the position.
I guess what I'm trying to say is just be prepared for everything you do, make a good first impression, and eye CONTACT always. even for the ho hum volunteer interviews.