To execute the foldover, place one palm on the small of the suspect's back and pull. Drive the palm of your other hand upward to strike the suspect's chin, forcing his head back. When his head is off axis of his body, the suspect's balance will be compromised and he will likely fall over backwards.
Remember that you've got to have leverage and momentum to be effective. For maximum leverage, make sure your lead foot is past the suspect's leg. You also need to shuffle forward to develop momentum while directing the suspect's head back and down.
The shoulder wrap is achieved by grabbing and pulling the suspect's far side shoulder and encircling your same-sided arm vertically around the suspect's arm. When both of your hands are placed on the suspect's shoulder, his shoulder and elbow will be unable to move. Step with your rear leg behind your lead leg and turn your upper body to face the same direction as the suspect while applying downward pressure on the shoulder. Using the suspect's arm as a lever, you are now able to direct the suspect into a prone position.
Momentum in this technique is developed not only by manipulating the shoulder but also by "opening the gate." Opening the gate refers to the action of stepping behind your lead leg and pivoting on the balls of your feet to spin roughly 180 degrees so that you are facing the same direction as the suspect.
This technique is proof that where the head goes, the body follows. To execute the head twist, simply place one hand behind the suspect's head and pull it toward your opposite shoulder. Use your other hand to drive the suspect's chin away. This action will cause the suspect's whole body to turn. Again, by opening the gate, you create a void for the suspect to fall into.
This technique won't be effective if executed lackadaisically. Only be forcefully pushing and pulling the suspect's head while performing the "opening the gate" footwork described above will you develop sufficient momentum.
Pain compliance techniques such as control holds and pressure point manipulation are effective methods for dealing with moderately resisting suspects. However, since these techniques tend to be based on fine-motor skills, they can be difficult to apply under stress. Additionally, they will be ineffective if the suspect does not feel pain. Since body mechanics techniques are more gross-motor based, they require less precision to execute. And, since their effectiveness is not dependent on the suspect's reaction to pain, they are usually the better option for dealing with a violent suspect.
Train hard. Stay safe!