Hi Lauraphx,
1) Keep the target in the shot when the target is standing. Be mindful not to stand too close to the target. By taking a few steps back you will widen the scope of the video getting more of the target without having to move so often. Keep your shoulders square to the target and just move your head as needed. For example, when you're both standing in the kitchen and the target points out the floor to ceiling windows at the far end of the room, just turn your head towards the windows and not your whole body. Remember, it's the target that the client want to see--not the windows.
2) Keep the target in the shot when the target is sitting. When the target invites you to have a seat at the desk, take care that your button cam is picking up the target and not merely the rim of the desk. You can make unobtrusive adjustments by simply moving your chair back to capture a wider frame, adjust the shoulders of your shirt so as to raise the button cam slightly, or keep standing and tell the target you've been driving so much your legs need a good stretch!
3) Practice at home to increase your confidence and attend one of the video conferences (VideoCon, IMSC, MSPA) to improve your skills.
4) Remember to format your SD memory card!
5) Modulate the tone, volume, and clarity of your voice, avoid incidental language, let the target take the lead, and avoid inadvertent body sway.