For business school interviews, you can't go wrong with a blazer and tie. Skype is slightly more casual; you can probably get away with just a shirt and tie, no jacket, since you're inside. But why risk it? After all, if you get to hot in a Skype meeting, you don't really need pants.
Additionally, think about what your backdrop will look like. If you can manage it, it's not a bad idea to hang a sheet behind you, just so you have something neutral in the background. Make sure that you don't have people, inappropriate posters, or even just messy clutter in the background when you're on video. It looks unprofessional.
Finally, a few camera tips. Sit at a desk--if you're looking down at the laptop camera in your lap, your head will appear cocked at a funny angle. And move the interviewers chat window to the point on your screen as close to the camera as possible. Your natural instinct is to look at that image, and if that image is too far from your camera, it will look like you're staring into space.
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