I've extracted parts from this article that seem relevant to people who may be reading about Vajrayana for the first time, or are brushing up on their knowledge. Please feel free to chime in with information if you see fit, or to ask questions. The entire article can be found here. Due to the length of the article, I've edited out a fair amount of information for this post.
"The Foundational Practices of Vajrayana: A Summary of the Essential Points"
Written by Dr. Yutang Lin in Chinese as Part 2 of "The First Steps of Vajrayana"
Translated by Stanley Lam
Reviewed and edited by Dr. Yutang Lin
All schools of Vajrayana teach certain foundational or preliminary practices (Ngondro) that enable practitioners to settle their minds in the Dharma, to remove karmic hindrances, and to increase merits and wisdom. Thereby novices will be able to make smoother progress on the path. Tantric teachings should be learned from authentic lineage teachers, hence the foundational practices are to be conducted as taught by a tantric teacher.
Nowadays Vajrayana Buddhism has propagated widely, and many practitioners are able to receive teachings of different lineages from various tantric teachers. Many teachings of the major traditions have also been published and are available in bookstores. As a result, we can learn from many sources to deepen our understanding of the theoretical aspects of the Dharma, and then digest and assimilate them into a correct view, so as to direct us on the path of practice.
I will report in this work the main points of my findings and understanding of the foundational practices so as to provide a practice manual for Dharma friends' references.
II. GENERAL OVERVIEW
There are two categories of foundational practices: common and uncommon. The former ones are condensed teachings derived from the common principles of Hinayana, Mahayana and Vajrayana, and are organized in a systematic way. Practitioners should begin by contemplating on these reasonings so as to develop a guiding thought toward diligent practice. The uncommon foundational practices are teachings specific to Vajrayana Buddhism, and their main purpose is to eliminate karmic hindrances and increase merits and wisdom.
A. Common foundational practices
I. Traditional teachings
They are classified into six points:
1) Recognize the rarity of the opportunity to practice the Dharma
2) Remember the impermanence of life
3) Observe the suffering of all sentient beings in the six realms
4) Believe in the law of Karma
5) Understand the superiority of the path to liberation
6) Rely on a qualified spiritual guide
The above classification is in accordance with the teachings of Nyingma tradition, while the Kagyu tradition lists only the first four. It is not enough just to understand these teachings. One must have thoroughly contemplated on them in concentration meditation so as to solidify them into central guiding thoughts. Only then would one be able to renounce worldly engagements and continue to practice diligently without regress.
B. Uncommon foundational practices
All Vajrayana schools of Buddhism in Tibet have their requirements for uncommon foundational practices. Those are usually called the Four Foundational Practices or Four Preliminary Practices (Ngondro) and constitute basic trainings prior to practicing any Highest Yoga Tantra (Anuttara Tantra) practice. The various schools have not exactly the same items of Foundational Practices. Even when the names of the items are the same, the details in content and the quantity required may vary. In general, the Four Foundational Practices amount to 100,000 (or 111,111) repetitions of each of the following four practices:
1) Taking fourfold refuge, usually including 100,000 great prostrations and 100,000 repetitions of the stanza of Generating Bodhicitta
2) Hundred Syllable Mantra (Vajrasattva Purification Practice)
3) Mandala Offering, usually the seven-offerings Mandala
4) Supplication prayer to lineage Gurus (Guru Yoga), may include mantras of lineage patriarchs
1. Functions of the Four Foundational Practices
The main function of the Four Foundational Practices is to purify negative Karma and to accumulate merits so that the practitioner will have sufficient resources to engage in practice without encountering obstacles and hindrances. Speaking in the given sequence: the foundation of faith is developed through taking refuge, generating Bodhicitta and doing prostration; the Karmic hindrances are purified through the Vajrasattva Purification Practice; wisdom and merits are accumulated through offering of Mandala; and lineage blessings are received through practicing Guru Yoga. Going one step further, each foundational practice may be liken to pouring pure water into a cup of muddy water. With perseverance, the water in the cup will eventually become all pure. Therefore, each foundational practice contains all four aspects of: a) refuge and faith, b) receiving blessings, c) purifying negative Karma, and d) increasing merits. Viewing in their entirety, all four foundational practices are mutually complementary in preparing the practitioner to become a crude model of a Dharma instrument.
2. Supplementary guidance of precepts
Using the analogy above of pouring pure water into a cup of muddy water, we can understand that, in order to obtain full benefits of the Four Foundational Practices, a practitioner also needs to prevent negative deeds, just as not adding any more muddy water and preventing the cup from leaking. Therefore, it is also necessary to take precepts and learn about proper conduct from the Guru. In general, the main precepts at this stage are: five precepts, ten virtues, Bodhisattva's vows, Tantric root precepts, fifty stanzas on attending the Guru.
3. Relationship among the Four Foundational Practices
This topic can be understood through the explanation given in the Functions of the Four Foundational Practices above. In summary, the relationships of the Four Foundational Practices are: each practice includes the effects of all four, and all four practices together complete the functions of each practice.
4. Relationship with practices that precede or succeed the foundational ones
The exoteric practices are skillful means in the position of cause, therefore the Paths of Accumulation and Preparation take one Asamkhyeya-Kalpa to complete. The Four Foundational Practices belong to Vajrayana which consists of skillful means in the position of consequence. When the Foundational Practices are properly carried out, the Accumulations can be perfected within a few years. This is the distinctive point of their superiority.
The common foundations are practices to develop foundations for a correct view; the uncommon foundations are the first steps of practice based on the correct view.
After completion of the Four Foundational Practices, one can progress further to the Development Stage practices and then the Perfection Stage ones. In fact, the Four Foundational Practices already include certain visualizations of the Development and the Perfection Stages, such as visualizing the bestowal of empowerment by the Guru and the union of Vajrasattva Father and Mother. However, those visualizations have been simplified to cater for the novices. The practice of great prostrations can straighten one's channels, thus laying a foundation for smoother wind and channel development in the Perfection Stage. Within refuge taking, Gelugpas also include the Nine Receptions of Buddha Wind, while the Nyingmapas sometimes include inhaling Karmic air of sentient beings and exhaling virtuous air to benefit sentient beings in order to cultivate Bodhicitta. Both of these are preparations for wind practices of the Perfection Stage.
5. Sequences of practicing the Four Foundational Practices
a. Complete 100,000 times of one practice before proceeding to another
The sequence of these practices varies with each school. Guru Yoga is the first one for the Gelugpas, and yet the final one for the Nyingmapas and the Kagyupas. The most common sequence is the one listed above, i.e., Refuge, Vajrasattva Purification, Mandala, and then Guru Yoga. However, it is not rigidly required to follow such an order, and the practitioner may arrange his or her own sequence.
b. Doing several practices concurrently
Sadhanas (ritual texts) of the Four Foundational Practices are usually arranged for practicing only one kind of such practices in a given session. Nevertheless, within one such Sadhana may be found two or three items that need to be repeated 100,000 times. For example, the practice of taking refuge may include great prostrations, and Guru Yoga may include supplication prayer to lineage patriarchs as well as the mantra of a lineage patriarch. Some Sadhanas also combine the four practices so that all four practices are taken up sequentially within each session.
The practitioner may also do several session of different practices each day. For example, when getting tired from doing prostrations, one switches to Vajrasattva purification; when getting tired from chanting, it is followed by Mandala offering. It would become easier to persevere in practice, when one adjusts physically and mentally in this way.
6. Key points that are common to all the Four Foundational Practices
a. Common basic trainings
Besides the common foundations as described in previous sections, we can conclude from the perspective of Three-Yanas-in-one (i.e., Hinayana, Mahayana, Vajrayana as a coherent, step by step, system toward total liberation) that the Four Foundational Practices share the following basic trainings: all phenomena as empty of independent existence, skillful application of Dependent Origination, and unification of concentration and observation in meditation. If a practitioner has sufficient meritorious Karma to enter Vajrayana without prior training in exoteric Buddhism, he or she should learn the essential teachings of Hinayana and Mahayana, especially to understand the concepts mentioned above and to practice the concentration and observation meditations.
b. Common objects of visualization
In the practices of taking refuge, prostrations, and Mandala offering, one visualizes holy beings forming a field of refuge. Each Vajrayana school has its particular field of refuge, but all of them consists of Gurus, Buddhas, Dharma, Sangha, Yidams, Dakinis and Dharma Protectors. Setting up an image of the field of refuge on the altar would help one in the visualization.
In both Vajrasattva Purification and Guru Yoga, the Wisdom Being above the practitioner's head is visualized to be identical to the Guru, who is also the essence of all holy beings and scriptures in the entire field of refuge. According to the oral instruction of Yogi Chen, one can visualize the face of the Vajradhara or Vajrasattva above one's head as that of the Guru in order to receive blessings. When reciting supplication prayer to the lineage Gurus whose appearances are not known, one can visualize all of them as Vajradhara.
When doing each practice, one should first visualize one's father by the right side and mother by the left side, all sentient beings related through Karma to the practitioner are in front, and all other sentient beings are encircling behind, in the order of hell beings, ghosts, animals, human beings, asuras, and gods. All these sentient beings are doing the same practice as the practitioner. At the end of the session, dedicate all the merits to each and every sentient being. This belongs to the Victorious Significance of the Bodhicitta of Conduct.
All these common visualizations are, based on the principle of the indifferentiability of mind and phenomena, to practice using the power of mind to purify phenomena, and to liberate the ordinary consciousness which is confined within the limits of phenomena. These visualizations are not conceptual imaginations; when the visualizations mature, one would experience lineage blessings and expand one's mind to the entire Dharmadhatu. Although beginners can seldom perfect the visualizations, as long as one has genuine Bodhicitta and immovable faith, one could still receive blessings from the holy beings. In addition, all objects of these visualizations should be like rainbow, vivid and yet without any concrete substance.
IV. COMBINING the FOUR FOUNDATIONAL PRACTICES IN ONE SADHANA
Following the above order of presentation, a practitioner may practice in one session all of: taking refuge (including three kinds of recitation), great prostrations, Vajrasattva purification, Mandala offerings, and Guru Yoga. The practitioner can determine the amount of repetitions of each practice during such a session based on the time available and the speed of each practice. This arrangement is suitable for lay practitioners in general who can practice only one session a day. If there is not enough time in each session, one may reduce the number of items practiced.