The effectiveness of meditation on the lamrim, the stages of path to Buddhahood, depends on the degree of one's preparedness, which is achieved by purification and accumulation of merit practises. "Purification" refers to the removal of the obstacles and harmful potentialities acquired by wrong thoughts, words and deeds, which interfere with one's progress; "accumulation of merit" refers to the creation of virtue, by beneficial thoughts, words and deeds; it ensures one of conditions favouring spiritual achievements.
Typically a lamrim meditation or teaching session is therefore preceded by the recitation and meditation on the six preliminary practices (Tib. sByor ba'i chos drug). Two works commonly used for this purpose are the Necklace of the Fortunate, a ritual compiled by Venerable Dagpo Rinpoche's predecessor, and the Preliminary Practices of the Southern Lineage Lamrim.
The first of the six preliminaries consists in cleaning the meditation room and setting up symbols representing the Buddha's body, speech and mind. The second is to set up offerings. The third is to sit in meditation posture, visualise the Buddha, take refuge and generate the spirit of enlightenment. The fourth consists in visualising the "merit field' –the assembly of Buddhas, lineage masters and so forth in relation to which one does the fifth practice, the seven-fold prayer for purification and accumulation of merit. The sixth preliminary practice is supplicating the lineage masters –the unbroken line of teachers from Buddha Shakyamuni until one's personal masters– for their blessings in the form of spiritual attainments.
On this basis next one meditates on the lamrim either concisely, using for example The Foundation of All Excellence, a prayer in verse by Je Tsongkhapa, or in greater detail, going into each successive topic. One concludes the preliminaries with a dedication prayer by which one transforms the good karma generated by the practice into causes of enlightenment.