Set-up: Step up close to the bar with shins touching or very close to touching the bar. Keep the shoulders back, get the hips low - but not lower than the knees, push the chest out, and look straight ahead. Brace through the core and maintain a strong neutral spine curve.
Lift: To begin the lift push through the heels. When the bar passes the knees begin to push your hips forward, reaching full hip-extension at the end of the lift. Lower the bar close to the body and under control. Maintain the neutral spine position throughout.
Emphasis: Do not round the back - particularly the lower back - at any time; the spine should be neutral throughout the movement. Do not hyperextend your lower back at the end portion of the movement - the lockout should come from the hips. Instead cue to fire your glutes at the end of the movement. Also be sure to keep the arms straight for the entire movement - there should be no bend in the elbows. The pull should be a coordinated movement and the shoulders should rise at the same speed as the hips.
Caution: Before deadlifting, make sure that you have adequate hip mobility. That is, make sure you are able to grasp the loaded barbell from the ground by hinging at your hips and keeping your back straight, and that you do not have to bend your lower back to achieve that range of motion. If you are unable to achieve this motion, you may need to 1) stretch your hip flexors and 2) begin implementing some light mobilization exercises for the hips. In the meantime you can train the posterior chain with other exercises, or perform the deadlift elevated from blocks or pins where the start position is still within the range of your safe mobility.