The first things I notice as an interviewer are lighting and background. So often there is something distracting in the background such as a window with open drapes or blinds blinding the camera to where I can't see the interviewee. Another common mistake is something distracting and unprofessional in the background like dirty laundry in the floor or general clutter. It makes no sense to put on a jacket and tie and then have an unprofessional presentation behind you. You can also focus the camera in to where you are just showing your face and upper body, not allowing the viewer to see anything behind you. If your camera doesn't focus just move it closer or further away until the picture looks right.
Also the lighting on your face is important; if your face is dark you come across as unfriendly, similar to if you are frowning vs. smiling. Having your face properly lit, and a smile on your face as you speak, gives an entirely different presentation.
Another issue I run into is camera angle. If like me you have a little more chin than you wish you had then you don't want the camera looking up at you from your desk. If you use a laptop place it on a stack of books. If you use a camera mounted on or continued within a monitor, angle the monitor for your best presentation of our face. For video interviews I use this setup.
Other than the physical setup just remember some of the basics. Have something to drink nearby in case you get choked; you can't cover the camera like you can cover the phone with your hand in a telephone interview. Have your questions prepared ahead of time, and relevant documents handy so you can refer to them if need be for specific questions.
Finally, speak slowly, confidently and with a smile. After just a minute or two you'll adjust to the face on the screen and start talking to it just like you were there in person.