This post is on technical advice.
Mudra is called Shuo Yin (Hand-symbol 手印) in Chinese. All meditative practices make use of Mudra. Tibetan practitioners even use complicated Mudras for curing different diseases. They have their points, as I shall explain.
In a previous post I suggested practitioners to try different Mudras to see their effects. The question is: what is the underlining or common skills in doing different kinds of Mudra?
In Zhan Zhuang for health purpose, a full hand stretch is generally preferred. One common visualization is holding a rubber ball, resulting in a balance between pressing in (by fingers) and bouncing out forces (by the imaginary rubber ball). Pressing in is Yang, and bouncing out is Yin. Yang and Yin must be balanced.
This kind of internal Yin/Yang balance must be maintained for each fingers during any Mudra. However, there is an additional requirement for Mudra that do not employ a full hand stretch. In these Mudras, some fingers need to be pressed-in more than other fingers. For example, in Bruce Lee's typical combat stance (check here to see), the middle finger together with thumb are more pressed in. These two are in Yang relative to the other Ying fingers. As a way of contrast, the Yin fingers will like pointing outwards. A stronger tension will be created by Bruce Lee's Mudra. Buddhism, and Tibetan in particular, will use more complicated Mudra for different purposes.
These Yin/Yang interaction will create different chi-patterns directed towards the body, and hence affecting a practitioner's internal organs or psychology differently. For a sensitive practitioner, he can therefore try different Mudra and feel for himself how each affects his internal conditions.