'Foundational Practices, Four (Tib. Chagchen Ngöndro) translates as 'the preparation for the Great Seal'; also named the Four Special Preliminaries.
With the Foundational Practices, one creates countless good impressions in the subconscious. They build the foundation for the Great Seal.
One completes 111,111 repetitions in each of the four meditations:
(1) Taking refuge and developing the enlightened attitude through prostrations,
(2) Purifying the impressions that bring suffering through the Diamond Mind meditation,
(3) Offering good impressions with Mandala Offerings,
(4) Meditation on the Lama (Guru Yoga).'
-- Quoted from 'Buddha & Love' book by Lama Ole Nydahl.
See also, if You wish: Ngöndro - Beyond the Comfort Zone.