A Skype interview should be treated like any video conference interview. Most importantly, you want to dress for the occasion just like you would for any office interview. Secondly, you want to make sure that you have a professional background behind you. A plain white wall is a good choice with no clutter behind you. Also, it's important that the interview take place in a quiet location so as to minimize any kind of distraction like phone rings and beeps.
Further, as with video conference interviews, you want to smile a lot and emote because personality doesn't come through as well on video. Also, you will want to make sure the interviewer is done with their question before you begin your answer, as it easy to talk over one another during a Skype conference. It's also a good idea to test your technology beforehand by doing a practice run with a friend to make sure your equipment is running properly, especially your microphone.