And whoever, at the end of his life, quits his body, remembering Me, attains immediately to My nature; and there is no doubt of this." (B.G.8:5) One who thinks of Kṛṣṇa at the time of his death goes to Kṛṣṇa. One must remember the form of Kṛṣṇa; if he quits his body thinking of this form, he surely approaches the spiritual kingdom.
(Bhagavad-Gita-introduction).

Of course, one's thoughts during the course of one's life accumulate to influence one's thoughts at the moment of death, so this life creates one's next life. If in one's present life one lives in the mode of goodness and always thinks of Kṛṣṇa, it is possible for one to remember Kṛṣṇa at the end of one's life. That will help one be transferred to the transcendental nature of Kṛṣṇa.
(Bhagavad-Gita----8:6----purport).

Yoga practice is meditation on the Supersoul within; similarly, by chanting Hare Kṛṣṇa one fixes his mind always on the Supreme Lord. The mind is fickle, and therefore it is necessary to engage the mind by force to think of Kṛṣṇa. One example often given is that of the caterpillar that thinks of becoming a butterfly and so is transformed into a butterfly in the same life. Similarly, if we constantly think of Kṛṣṇa, it is certain that at the end of our lives we shall have the same bodily constitution as Kṛṣṇa.
(Bhagavad-Gita----8:8----purport).

One should think of Kṛṣṇa and act for Kṛṣṇa favorably, not unfavorably. Kaṁsa was an enemy of Kṛṣṇa's. From the very beginning of Kṛṣṇa's birth, Kaṁsa planned in so many ways to kill Him, and because he was always unsuccessful, he was always thinking of Kṛṣṇa. Thus while working, while eating and while sleeping, he was always Kṛṣṇa conscious in every respect, but that Kṛṣṇa consciousness was not favorable, and therefore in spite of his always thinking of Kṛṣṇa twenty-four hours a day, he was considered a demon, and Kṛṣṇa at last killed him. Of course anyone who is killed by Kṛṣṇa attains salvation immediately, but that is not the aim of the pure devotee.
(Bhagavad-Gita---11:55----purport).

External cleanliness means taking a bath, but for internal cleanliness one has to think of Kṛṣṇa always and chant Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare. This process cleans the accumulated dust of past karma from the mind.
(Bhagavad-Gita---13:8-12----purport).

The Sanskrit word mat-paraḥ is very important in this verse. It indicates that one has no goal in life save and except acting in Kṛṣṇa consciousness just to satisfy Kṛṣṇa. And while working in that way, one should think of Kṛṣṇa only: "I have been appointed to discharge this particular duty by Kṛṣṇa." While acting in such a way, one naturally has to think of Kṛṣṇa. This is perfect Kṛṣṇa consciousness.
(Bhagavad-Gita---18:57----purport).

One should not become an official meditator. Life should be so molded that one will always have the chance to think of Kṛṣṇa. One should always act in such a way that all his daily activities are in connection with Kṛṣṇa. He should arrange his life in such a way that throughout the twenty-four hours he cannot but think of Kṛṣṇa. And the Lord's promise is that anyone who is in such pure Kṛṣṇa consciousness will certainly return to the abode of Kṛṣṇa, where he will be engaged in the association of Kṛṣṇa face to face.
(Bhagavad-Gita---18:65----purport).

Therefore directly or indirectly anyone who thinks of Kṛṣṇa, talks of Kṛṣṇa or worships Kṛṣṇa becomes attached to Him. Because Kṛṣṇa is absolute, there is no difference between His name, form, quality, etc. Our intimate relation with Kṛṣṇa can be confidentially revived by our talking of, hearing of, or remembering Him. It is so done due to spiritual potency.
(Srimad Bhagavatam----1:10:14----purport).

The main purpose of sannyāsa life is to be in constant companionship with the Supreme Lord, either by thinking of Him within the heart or hearing of Him through aural reception. In this age, hearing is more important than thinking because one's thinking may be disturbed by mental agitation, but if one concentrates on hearing, he will be forced to associate with the sound vibration of Kṛṣṇa. Kṛṣṇa and the sound vibration "Kṛṣṇa" are nondifferent, so if one loudly vibrates Hare Kṛṣṇa, he will be able to think of Kṛṣṇa immediately.
(Srimad Bhagavatam----3:24:35----purport).

A devotee should not be greedy. It is also recommended that the devotee should be muni, or thoughtful; he should always think of Kṛṣṇa and how to render better service to the Supreme Personality of Godhead. That should be his only anxiety.
(Srimad Bhagavatam----3:27:8----purport).

The conditioned soul has a false ego, and as a result of his karma he gets different types of bodies in this material world. Sometimes he gets the body of a demigod, and he thinks that body to be his identity. Similarly, when he gets the body of a dog he identifies his self with that body. But for the Supreme Personality of Godhead there is no such distinction between the body and the soul. Bhagavad-gītā, therefore, certifies that anyone who thinks of Kṛṣṇa as an ordinary human being is without knowledge of His transcendental nature and is a great fool.
(Srimad Bhagavatam----4:11:25----purport).

The process of Kṛṣṇa consciousness, by which one always thinks of Kṛṣṇa, is the transcendental process by which one can revert to his original, spiritual existence. Devotional service means always thinking of Kṛṣṇa.
(Srimad Bhagavatam----4:29:75----purport).

The root cause of one's association is the mind. This great Kṛṣṇa consciousness movement is the greatest boon to human society because it is teaching everyone to think always of Kṛṣṇa by executing devotional service. In this way, at the end of life, one may be transferred to the association of Kṛṣṇa.
(Srimad Bhagavatam----4:29:76-77----purport).

This Kṛṣṇa consciousness movement is therefore the greatest boon to humanity because it keeps one always engaged in Kṛṣṇa's service. The devotees think of Kṛṣṇa, act for Kṛṣṇa, eat for Kṛṣṇa, sleep for Kṛṣṇa and work for Kṛṣṇa. Thus everything is engaged in the service of Kṛṣṇa. A total life in Kṛṣṇa consciousness saves one from material contamination.
(Srimad Bhagavatam----4:30:19----purport).

Whereas materialists are absorbed in material thoughts and activities, devotees, on the contrary, are always absorbed in thoughts of Kṛṣṇa and Kṛṣṇa's activities. Therefore they are already on the platform of liberation. One has to think of Kṛṣṇa with full absorption at the time of death. Then he will certainly return home, back to Godhead, without a doubt.
(Srimad Bhagavatam----5:19:13----purport).

This means that one must accept a spiritual master who comes in the disciplic succession and is a servant of the servant of the Lord. Under his direction, one must then engage one's three properties, namely his body, mind and words. The body should be engaged in physical activity under the order of the master, the mind should think of Kṛṣṇaincessantly, and one's words should be engaged in preaching the glories of the Lord. If one is thus engaged in the loving service of the Lord, one's life is successful.
(Srimad Bhagavatam----6:11:24----purport).

The advantage of Kṛṣṇa consciousness is described herein. Kṛṣṇa consciousness gradually develops on the transcendental platform. One may think of Kṛṣṇa as the supreme personality, one may think of Kṛṣṇa as the supreme master, one may think of Kṛṣṇa as the supreme friend, one may think of Kṛṣṇa as the supreme son, or one may think of Kṛṣṇa as the supreme conjugal lover. If one is connected with Kṛṣṇa in any of these transcendental relationships, the course of one's material life is understood to have already ended. As confirmed in Bhagavad-gītā (4.9), tyaktvā dehaṁ punar janma naiti mām eti: for such devotees, going back home, back to Godhead, is guaranteed. Na punaḥ kalpate rājan saṁsāro jñāna-sambhavaḥ. This verse also guarantees that devotees who constantly think of Kṛṣṇa in a particular relationship will never return to this material world.
(Srimad Bhagavatam----10:6:39-40----purport).