There are several ways to train wardoff jing. A good way is to use a bag, first a light one and later, heavier ones. You can practice striking with wardoff, and you can practice pushing. To do the latter, you can place your forearm against the bag and push it slightly to get it moving. "Catch" the bag on your forearm as soon as it starts to move toward you, and immediately bounce it away. You can swing the bag and "catch" it near the end of its swing and bounce it, or move the bag around in circles and use wardoff to redirect it sharply away from you.
You can also practice wardoff on a partner. When you do this, it is best for the person being pushed to protect his chest with his forearms to prevent injury. Another exercise is for one person to stand in the wardoff position, and the other to push the extended forearm with both hands in a somewhat stiff-armed fashion. The first person either absorbs some of the force, directs it into his root, and then bounces it back, or else emits force just as the other person is about to push. Click to learn how Chinese medicine treats Lung Abscess.
When doing wardoff, the body must be centered and stable, and your yi of attacking must be farther than the target. Yi, qi, and jing must be balanced among the attacking arm, the other arm, and the rear foot.