Stance adds to image
quality, a bad stance can lead to camera shake. Place your feet shoulder with
apart and one foot slightly infront of the other, relax.
Your stance is not only important when taking a picture unsupported but also when using supports such as beanbags, monopods, walls, cars and even tripods. If your not sufficiently stable in your stance then any movement is transmitted into anything you are touching or holding ie. your camera.
When using a tripod position the tripods legs so you can get within the legs and close to the centre of the tripod and your camera. Always try to use a cable release and reframe from touching the camera or tripod. See however details on working with Super telephoto's for exceptions to this.