Proper compressions are essential to providing good quality CPR. Often times people have difficulty with proper hand placement and depth. Believe it or not, good compressions are actually less stressful on the body and you can do more of them. Bad compressions are not only ineffective, but tiresome because they distribute a majority of the workload on weaker muscles instead of using the advantage of your body weight as described below. The following information demonstrates how to perform good compressions.
Check for Signs of Movement
If no movement is found, start chest compressions. If Movement is Found, Place the Patient in the HAINES Recovery Position
Compressions
Place the heel of your dominant hand in the center of the chest and place your other hand interlocked over the top of that hand. Compressions should be done in intervals of 30 at a rate of at least 100 times per minute and at a depth of 1.5-2.0 inches or 1/3 to 1/2 the depth of the chest. Do not get caught up in the technical details, JUST PERFORM THE COMPRESSIONS. INTERRUPT COMPRESSIONS AS LITTLE AS POSSIBLE. Continue CPR at a ratio of 30 compressions and then 2 breaths.
The biggest mistake in performing compressions is not pressing hard enough! Improper compressions are characterized by arms bending and improper hand placement as shown below:

(Poor Compressions)
Proper compressions are characterized by good depth, straight arms, using your shoulders and interlocking your hands as shown below:

(Good Compressions)
Video Resource