Tip #7, communicate with your subject.
Tip #7 for capturing the sharpest images: Good communication.
The most common cause of blur in photos is movement, right? Not all movement comes from the camera. In the portrait studio, I will typically let my subects know before I take each shot so they hold as still as possible.
I love using this photo of Rachel as an example. She would be adjust her outfit or looking around the room or doing whatever. As soon as I told her I was ready for the shot, she snapped into pose and brought her eye directly to the focus square with pinpoint precision. Impressive!