I applied online in the autumn for a summer internship. The online application is extensive and time-consuming. A few weeks later I got an e-mail requesting a phone interview with the specific office that was interested in my application. It was a little bit difficult to schedule the interview, as I was in California and the Embassy was in Europe, so it was a little tough to find a time that fell within normal business hours in Europe and waking hours in California.
When the actual interview came, the discussion focused primarily on my previous experience. I felt that confident answers and speaking well were two things that helped during my interview. My interviewer also liked to see writing experience, particularly with deadlines and concise style. Customer service and the ability to work well with others and as a team also seemed to be pluses. Leadership, communication, and social skills were points of emphasis.
I didn't face too many tough questions-- mostly about why I wanted the position, why I chose my field of study, why I requested the particular office and position I selected, what my strengths are, etc. I was also asked things like if I would be comfortable finding my own housing in a foreign country if necessary and other such things related to accepting an overseas internship.
Soon after, my interviewer requested another phone call. I was prepared for another round of interviews, but after a few short questions they offered me the position. I accepted and it was one of the most enriching and rewarding experiences of my life.