Skype is fine. Find a friend who is a native speaker to practice with you beforehand. The key of practice is walk you through a standard interview and clam you down. Most of time, people tend to over think and over stress about school interviews.
At the very least, you should be prepared to discuss your three most significant:
1>academic and professional accomplishments and what they mean to you 2> personal strength and weakness 3) abilities that will make you an excellent leader or/and teammate 4>challenges from professional and personal life 5>why you are a such a great fit for the program