Set-up: Set up inside of a power-rack and set the safety pins to just above hip-height. Put the bar on pins at a point that is easy to contact, somewhere between your shoulders and the middle of your back. Set your feet slightly wider than shoulder width apart and point your toes out slightly - in-line with your knees. Duck underneath and in front of the bar, raise your chest, brace your stomach and establish a netural spine posture. Grip the bar with your hands at roughly twice shoulder width. Select the grip that gives you the most control and stability. Now lift the bar out of the pins driving through the legs.
Lift: While maintaining a neutral spine position and tight brace through the core, descend as far as possible without rounding your lower back. For most this will be when the hips are 3-12 inches below the knees. Drive the weight up in a straight-line.
Emphasis: Brace through your core at all times. Keep a neutral spine throughout the duration of the movement - if a neutral spine cannot be maintained, either reduce the weight or shorten the range of motion. Do not let the knees cave inward on the movement. Attempt to 'spread the floor' with your feet.