If you do your deadlifts incorrectly, you may be preventing yourself from seeing the results you are looking for as well as being dangerous.
Keep the bar level with the center of your foot. Next, bend down with your knees so that the bar is level with your shins. Your shoulders should be in a vertical line right above the bars. Now hold the bar down low and keep your hips up high. Then lift up your chest but do not contract your shoulders.
When you are pulling the bar up you want to keep it as close as you can to your body, trying to pull it back instead of pulling it straight up. Be sure to plant your heels firmly. That will help you to keep your center of gravity while you are lifting and lowering at a fast pace.