If the back is the most important body part in bodybuilding, then the deadlift is the most important exercise in the sport. The deadlift is one of the most effective exercises known to man. It stimulates the upper and lower back, as well as the legs, glutes, arms, and other body parts as well. It is one of the big three mass-builders, along with squats and bench presses.
The mechanics of the deadlift are remarkably simple: Pick up the barbell. Stand over the barbell on the floor. Grab the bar with a medium grip, knees slightly bent. Bring up the weight in a controlled motion, and then lean back at the end of the movement to lock out for just a second. Then slowly move the weight back to the ground. The legs drive the weight up, and the back stabilizes the body during the entirety of the movement.
If you find that the grip gives out before the lower back in this exercise, which is very common in Ectomorphic (skinny) trainers, use chalk and wrist wraps to help hold onto the weight. Very often, the hands and forearms are the weak link in the exercise, which short-circuits back muscle gains.
The back should be vertical, and tight. Movement of the weight should be in a controlled, slow manner. There should be no jarring effort. The back should never be rounded. Rather, the head should be up, leading the back to be upright and ready to move the weight without placing undue risk upon the spinal cord.
Source: www.BodybuildingToday.com