Prabhupada's lecture - Śrīmad-Bhāgavatam 1.5.36 - Vṛndāvana, August 17, 1974
So we have to work according to our capacity, at the same time chant Hare Kṛṣṇa mantra. Kṛṣṇa has given you the tongue, and there is no difficulty. Kurvāṇā yatra karmāṇi. And always think of Kṛṣṇa, man-manā bhava mad-bhaktaḥ. "How I can think of Kṛṣṇa constantly? It becomes hackneyed." No, the varieties. Kṛṣṇa says that you think of Kṛṣṇa while drinking water, you think of Kṛṣṇa when you see the sunshine, think of Kṛṣṇa when you see the moonshine, day and night. So at daytime there is sunshine, at night there is moonshine. So day and night you can think of Kṛṣṇa. So, so many ways... Kṛṣṇa-śikṣayā, bhagavac-chikṣayā, as He has taught in the Bhagavad-gītā, you think of always Kṛṣṇa. Then your life is successful. Man-manā bhava mad-bhaktaḥ. "How I can think of Kṛṣṇa constantly?

It becomes hackneyed." No, the varieties. Kṛṣṇa says that you think of Kṛṣṇa while drinking water, you think of Kṛṣṇa when you see the sunshine, think of Kṛṣṇa when you see the moonshine, day and night. So at daytime there is sunshine, at night there is moonshine. So day and night you can think of Kṛṣṇa. So, so many ways... Kṛṣṇa-śikṣayā, bhagavac-chikṣayā, as He has taught in the Bhagavad-gītā, you think of always Kṛṣṇa. Then your life is successful. Man-manā bhava mad-bhakto mad-yājī māṁ namaskuru [Bg. 18.65]

So therefore bhakti-yoga means vairāgya-vidyā. You have to stop thinking of this material bhukti, mukti, siddhi. Simply you have to think of Kṛṣṇa. That is spiritual platform. That is instructed here. Try to follow and your life will be successful.
Thank you very much.