The best way to stand for a picture is relaxed, with good posture, at a slight angle. The body shouldn’t be tense. Relax your hands, arms, and shoulders, and the rest of the body will follow.
Search for angles that look natural, and show off your best sides. If you don’t angle to the side, then lean forward slightly. It helps create a connection with the camera. A photo taken too straight on risks looking like a mugshot.
When posing for a headshot the focus should be on your face, always. The body is secondary to the facial expression.