ngondro is tibetan - ngon (before) dro (to go) aka preliminary practices aka foundation practices

A set of common and uncommon preliminary practices, beginning with the four thoughts that turn the mind away from saṃsāra and continuing with taking refuge, generating bodhicitta, maṇḍala offering, Vajrasattva visualization and mantra recitation, and guru yoga.1

turning confusion into clarity is a book on ngondro i recommend, in the book you are also introduced to subsequent practices called dzochen and the main parts of dzogchen meditation called shamatha and vipassana which are very penetrating and direct

ngondro (rigpa wiki)

four thoughts that turn the mind

turn the mind away from samsara

aka four common foundation practices

  • precious existence
  • impermanence
  • karma
  • suffering

the four unique foundation practices

  • taking refuge
  • purification
  • mandala
  • guru yoga

ngondro is the foundation for dzogchen if you skip it that's like building a castle on a fragile pond covered with a thin layer of ice

Purifying the Obscurations

It is sometimes said that

  • prostrations remove the obscurations associated with the body,
  • recitation of the hundred syllable mantra removes obscurations associated with speech,
  • mandala offering removes obscurations associated with mind, and
  • guru yoga removes the obscurations of all three: body, speech and mind.

Signs that the Common Preliminary Practices Have Penetrated the Mind2

by Nyala Pema Dündul

If you can devote your body unstintingly to the practice, That is a sign of taking to heart the preciousness of the freedoms and advantages.

If you can view gold and dirt with equanimity and see them as equal, That is a sign of having realized the illusory nature of transient things.

If you can regard the phenomena of samsara as your enemies, That is a sign of crossing over the ocean of suffering.

If you can pay meticulous attention to your actions and their effects, adopting virtue and abandoning non-virtue, That is a sign of finding the swift path that ascends the staircase to liberation.

If you can purify the negativity, defilements and habitual tendencies of your body, speech and mind, That is a sign of closing the door to rebirth in saṃsāra’s lower realms.

If you can keep the Three Jewels in your mind, so that they are never separate from it, That is a sign of being hooked by the compassion of the supreme refuge.

If you know how to integrate emptiness and compassion in your mindstream, That is a sign of bringing phenomena into the essence of awakening.

If you can meditate on how all beings have been your parents, That is a sign of the arising of the sun and moon of the great vehicle.

If you can dispel the obscurations of the darkness of ignorance, That is a sign of the dawning of clear light within immaculate space.

If you can carry the two accumulations onto the path continuously, That is a sign of the maturing of the fruition of kāyas and wisdoms.

If you can see all that appears and exists arising in total purity as the lama, That is a sign of reaching the pinnacle of Dzogchen yoga.

If you can recognize the vajra kāya of all-penetrating pure awareness, That is a sign of transference into the timeless space of primordial purity.

If you can recognize the unity of the three kāyas in pure awareness, That is a sign of the ripening of the fruition, which is Samantabhadra.

This brief summary of the signs showing that the common preliminary practices have penetrated the mind Was written in response to repeated requests from the assembly of my students, By the old beggar called Dündul. Through this merit may all beings be matured and liberated!