There is a great deal of literature on the theory and method of Xingyi practice. Unfortunately, they are mostly in Chinese. Recently some of those source material have been translated into English. The old, Emptyflower.com site did a remarkable job highlighting some of the key points of those Xingyi Classics. Ottawakungfu.org have reproduced their work since the site went dark.
Essential Knowledge for the Practice of Marital arts
by Dai Long Bang, 1750
Solo and Partner Practice - For those practicing martial arts, eighty percent of the time is spent in solo practice, twenty percent of the time is spent with others. Therefore, it is said, "The time strengthening the body is long, the time defeating opponents is short."
Daily Practice - One must practice every day, barring illness, without break.
Humility - One must not show off or bully others.
Quality vs Quantity - One who practices too great a variety will become panicked and distraught , if one does not train the body with a realistic foundation, in combat there will be no mature technique to fall back on, one will have neither a well trained body nor a solid technique.
Perseverance - There are those who have no perseverance, who study a little and think they know it all, they are quite satisfied with themselves and rarely practice, they think they are a great success, until they have to use the art and find themselves useless.
Before practice - The stomach should be neither too full or too empty, the mind should not be preoccupied with other affairs, do not practice when angry. When hungry one has no energy, too full and the stomach will be injured. Extraneous thoughts harm the brain. Anger harms the spirit.
During practice - Do not fool around. Do not spit. Do not be disrespectful. If one is not serious in practice the spirit is dispersed, spitting inflames the throat, disrespect weakens the practice.
After practice - Do not eat or drink, do not relieve yourself, do not lay down. Food and drink will not digest well, elimination causes qi to scatter, laying down causes the qi to rise causing discomfort.
The Three Harms - Those who practice martial arts must avoid the three harms.
1 - Inappropriate use of strength
2 - Forcing of breath
3 - Sticking out the chest and pulling up the belly
If one uses strength inappropriately, the qi will not flow smoothly, the meridians will be obstructed and the body will become bogged down. If one forces the breath, one will become stiff and easy to break, with the chest full of air the lungs will be squeezed and will suffer harm. If one sticks out the chest and sucks in the belly, the qi will move the wrong direction and will rise, it will not return to the dan tian.
Seeking Instruction - In order to study martial arts, one must be diligent in two areas. First, one must be willing to travel great distances in order to study with those of higher ability and sincerely request instruction. One must also be diligent in speech, humbling the self and asking for guidance.
Force and Self-satisfaction - In practicing the martial arts there are two things which must be avoided, the first is reliance upon force, the second is self-satisfaction.
Start Practice Slowly - After a period of practicing slowly, it is good to use more force and speed in order to increase the internal power for practical purposes.
Sequence of practice - At the beginning of practice stand in San Ti, then practice forms.
Stages of Training - After beginning formal practice, one must follow the rules of training, if so, in three years the basic training will be complete. In the intermediate stages of training, practice single forms repeatedly, use the form to express the intent. After a long period of practice one will be able to change spontaneously with the circumstances. After six years one will complete this level of training. In advanced stages of training, both the internal and external gong fu will be completed, your body will become as hard as steel, your gong fu will be of a high level.
Pictured: Dong Zi Ying
From the excellent book: "Xing Yi Nei Gong" by Tim Cartmell and Dan Miller.
When practicing, imagine as if you are facing a top fighter. However, in real combat, the mind is calm, and the face is not angry. "Be like there´s no one in front of you". The body remains relaxed at all times. Whole body power cannot be used with tense muscles and a worried mind. The body strikes in the manner of a bamboo pole: It´s flexible before reaching the opponent, and at the time of contact, the whole body tenses for a second, and the strikes come out with shocking force.
The important point is to keep the eyes alive, the body must be ready to follow the intention and keep the distance. If the opponent doesn´t move, the Xingyi practitioner doesn´t move. If the opponent makes one little movement, or hesitates, thus closing the distance, the Xingyi fighter advances with quick steps, breaking the enemy´s defense, and strikes him, with multiple attacks or simultaneous attack and defense, gaining space and not letting him step away from the attack, until the enemy is down. The mindset is finishing the encounter as soon as possible.
If the Xingyi fighter attacks first, he/she won´t let the enemy even know where the attack's coming from. One hand shows up, creating a reaction in the opponent. Based on that reaction, the Xingyi technique changes, attacking in many different ways, with shocking strikes that hurt, no matter where they land. (Because of its shocking nature, even a strike on the shoulder will transfer energy to the neck of the opponent, shaking his head with extreme force). Then, a fast takedown will finish the fight.
Xingyi trains the fighter to attack with every part of the body, specially with the "Seven Stars" (Head, Shoulder, elbow, hand, hips, knees and feet). Together with the whole body, they form the "Fourteen Fists". The fist come out like a shooting arrow, with force and vicious speed. The head, shoulders, hips and knees are very dangerous in close combat. Any of this parts of the body, being trained with the practice of Xingyi, can deliver a dangerous strike.
In standing grappling situations, the Xingyi fighter does not spend too much time. He uses attacks to break the hold by striking the opponent, followed with techniques intended to finish the fight before the enemy tries to grapple again.
Xingyi is a devastating fighting art, training the individual to strike even as he retreats, or turns.
Generally the fighting stance is a 45° position, with one foot ahead of the other. This protects the 'gates' of the body, because they are more hard to see, this way. Also, a smaller target is presented in this position. In addition to that, in this way is easier to move into the opponent´s range.
With all this in mind, one can understand how an art like Xingyi has stood the test of time. From the Chinese soldier on the battlefield to the modern day practitioner, this no-nonsense aggressive fighting art excels at what martial arts were created for, not health or character development ... but striped down highly effective fighting.