A mudra is a technique of Hatha Yoga. A mudra is essentially a ritualized gesture during an asana. It is highly advanced yoga. The skills required to perform a mudra are: proper breathing, competence in the asana in which the mudra is to be performed, and finally competence in the mudra itself. Because of this, training in mudras is undertaken while sitting: the lotus, the comfortable seat, and the kneeling positions are preferred for mastering a mudra. When a mudra is perfected, it may be easily applied to other asanas.
Natyasastra (the performance and passive arts) are typically relied upon for training in mudra, but training may also be achieved through other sastras may be utilized with success. The theory upon which all mudra function is that communication, if properly accomplished, can dynamically link two or more individual minds, can perfectly convey concepts and information, can transport a being to and from various lokas (worlds, or states of being), facilitate abstract logic and reasoning, accomplish all four jhanas, permit temporary or permanent enlightenment instantaneously - and thereby permit a person to realize the goal of practice more easily.
Such communication is accomplished both inwardly and outwardly, with other beings and with non-beings, in the same or different timeframe, in the same or different space, and/or in the same or different loka. Because of this facility, if perfectly performed, it can restore every being, and every loka, across space and time.
This is accomplished by action of agency representation: the actor represents the intended recipient of communication, becoming the vehicle, or vahana, of the recipient. This transformation of the communicator is accomplished through a sacrifice ceremony: they become the servant of the recipient by sacrificing their own distinct identity - and assuming another, as required by the recipient.
The mudra requires mastery of Maya, of delusion and illusion. For this, the skills of drama, music, dancing, drawing, writing, composition, and similar arts are studied: just as an actor might don a costume and the mannerisms of another, just as an artist would deceive the senses with illusions, the communicator must actually become a limb of the one they would serve, the recipient. In mastering Maya, the communicator begins to understand other perspectives: what is is like to be a man or a woman, to be a child or an old person, to be a non-human - and becomes capable of understanding what it is like to be the recipient. In order to prevent the likely self-injury of self-delusion, the communicator must also study and master the warlike defensive arts, the arts of debate and argument, and especially logic.
To guide another to moksha (the goal of mudra), the yogi need not have accomplished the journey themselves if they perfectly perform the sacrifice of self to the service of one who has: becoming the instrument of another, becoming the paint of another. Therefore, special attention must be placed on studying the rituals of sacrifice.
The yogi, having perfected their training in a murda, then applies it. The first step in application is to inspire love, friendship, wonder or curiosity - this creates a link between the communicator and the recipient. Then, the recipient is suspended from their loka through the enchantment of Maya: teasing apart the binds of mind, body and heart, so that each may function freely of the others. This then permits guided analysis of each component: mind, body and heart; and eventually guided analysis of each component of the mind, each component of the body, each component of the heart, with the effect of total disassociation and dehabitualization. When this is accomplished, the recipient is prepared to be transported to every space in each and every world, across every time; when thus delocalized, beyond space and time, beyond identity and self, the communicator may perform a transmission of Dharma: the recipient is guided into the first jhana, the second jhana, the third, the fourth. The recipient realizes Buddhi, Siddhi and Riddhi. At last, the connection must be broken: the connection between communicator and recipient must be done equally carefully. The bonds of Maya, now functioning like an umbilical cord, must be cut by the recipient - however, this may be encouraged and guided by the communicator.
The most basic mudras are accomplished by practicing finger movements, but more advanced mudras are accomplished by practicing coordinated movements in all the body. The most advanced practice involves control of autonomic functions: this typically begins with swallowing, breathing and blinking practice.
If you can understand how to communicate to others, how to communicate to yourself, how others understand things, how you understand things, you can begin to carefully perfect a mudra. Words remain the easiest and best form of communication: combine them with gestures, as a beginning. Say "thank you," say thank you and smile, say thank you and smile and gesture with your hand openly in welcome, and so forth. Learn to laugh, to sing, and make a person feel welcome. Learn to say "I love you," "you are a good friend." This is enough of a start.