There are regulative principles governing the renounced order. One has to perform eight kinds of śrāddha. One must offer oblations to one's forefathers and perform the sacrifice of virajā-homa. Then one must cut off the tuft of hair called a śikhā and also give up the sacred thread. These are preliminary processes in the acceptance of sannyāsa, and Svarūpa Dāmodara accepted all these. However, Puruṣottama Ācārya did not accept the saffron color, a sannyāsī name or a daṇḍa, and for this reason he retained his brahmacārī name. Actually Puruṣottama Ācārya did not accept the sannyāsa order formally, but he renounced worldly life. He did not want to be disturbed by the formality of the sannyāsa order. He simply wanted to worship Lord Śrī Kṛṣṇa without disturbance; therefore with heart and soul he took up the renounced order but not the formalities accompanying it. Renunciation means not doing anything but serving the Supreme Personality of Godhead, Śrī Kṛṣṇa. When one acts on this platform, trying to please the Supreme Personality of Godhead, one is both a sannyāsī and a yogī.
(Sri Caitanya Caritamrta-----2:10:108-----purport).

One must then chant the mantra of six syllables (oṁ viṣṇave namaḥ). One should place the syllable "oṁ" on his heart, the syllable "vi" on the top of his head, the syllable "ṣa" between his eyebrows, the syllable "ṇa" on his tuft of hair (śikhā), and the syllable "ve" between his eyes. The chanter of the mantra should then place the syllable "na" on all the joints of his body and meditate on the syllable "ma" as being a weapon. He should thus become the perfect personification of the mantra. Thereafter, adding visarga to the final syllable "ma," he should chant the mantra "maḥ astrāya phaṭ" in all directions, beginning from the east. In this way, all directions will be bound by the protective armor of the mantra.
(Srimad Bhagavatam-----6:8:8-10-----purport).

To take protection from this shield, one must first touch kuśa grass and wash one's mouth with ācamana-mantras. One should observe silence and then place the eight-syllable Viṣṇu mantra on the parts of his body and place the twelve-syllable mantra on his hands. The eight-syllable mantra is oṁ namo nārāyaṇāya. This mantra should be distributed all over the front and back of the body. The twelve-syllable mantra, which begins with the praṇava, oṁkāra, is oṁ namo bhagavate vāsudevāya. One syllable should be placed on each of the fingers and should be preceded by the praṇava, oṁkāra. Thereafter, one must chant oṁ viṣṇave namaḥ, which is a six-syllable mantra. One must progressively place the syllables of the mantra on the heart, the head, between the two eyebrows, on the śikhā and between the eyes, and then one should chant maḥ astrāya phaṭ and with this mantra protect himself from all directions. Nādevo devam arcayet: one who has not risen to the level of a deva cannot chant this mantra. According to this direction of the śāstra, one must think himself qualitatively nondifferent from the Supreme.
(Srimad Bhagavatam--6:8-----summary).