To learn how to fajing externally you only have to follow the steps for doing so. No big secret here except to those who don’t know what they are looking at. But this is not unusual considering that many practitioners are ignorant about classical mechanics.
To learn how to fajing internally is more problematic because on top of following the step-by-step instruction you also need to feel carefully what is going on in your body.
The clip below is taken at the earlier part of the lesson. To learn to fajing requires my student to remember to do the steps carefully, leaving nothing out, and feeling what is happening to ensure compliance to the process.
At the same time I have to put my hands on his arms to feel that he is adhering to the process properly. But as you can see this is easier said than done.
Towards the end of the clip I moved through the process a few times to allow him to feel how the force is moving through my body before gathering at my fist, waiting to be unleashed.
As illustrated, the double punch at the end of the Wu style long form can be used to train the fajing process.