Specific warm-up: Use a series of light sets, getting progressively heavier, to build up to your working weight.
Set-up: Find a spotter. Lie down on the bench with your shoulder blades retracted, your stomach and abs tight and your feet flat on the floor. Grip the bar several inches closer than shoulder-width (closer grips will put progressively more tension on the triceps, but at the price of positioning and stability).
Lift: Lower the bar in a straight line to your chest, keeping the elbows close to the body, until it just slightly touches the chest. Reverse the movement quickly while making sure the bar travels in a straight line back up.
Emphasis: Keep your shoulder blades together at all times and do not allow your shoulders to roll forward during the movement. Press the bar to your chest, NOT your face. Do not bend your wrists, there should be a straight line through your forearm up to your knuckles. Unrack the weight with straight arms.