I had a couple of Skype interviews with advisor about motivation, English level, technical knowledge, and how I see myself in 10 years. I was asked a couple of questions on how do I solve problems, and how do I work in teams. Part of the interview was bound to show me what the advisor would expect from me, and if that job was something I was interested on doing. The other requirements were a motivation letter, the transcripts, two recommendation letters, and GRE and Toefl scores

Meet with the professor that would hire you as an RA. I got invited into his office and started the interview process. It was a reasonable interview and I was pleased with it.