Nowadays there are so many yoga schools to encourage people in developing their lusty desires and greed through the practice of yoga. People are therefore very much fond of so-called yoga practice. The actual practice of yoga, however, is described here. As authoritatively stated in the Srimad-Bhagavatam (12.13.1), dhyanavasthita-tad-gatena manasa pasyanti yam yoginah: a yogi is one who always meditates on the lotus feet of the Supreme Personality of Godhead. This is also confirmed in the Brahma-samhita (5.38):

premanjana-cchurita-bhakti-vilocanena
santah sadaiva hrdayesu vilokayanti
yam syamasundaram acintya-guna-svarupam
govindam adi-purusam tam aham bhajami

“I worship Govinda, the primeval Lord, who is Syamasundara, Krsna Himself, with inconceivable innumerable attributes, whom the pure devotees see in their heart of hearts with the eye of devotion tinged with the salve of love.”

The bhakti-yogi constantly sees Syamasundara — beautiful Lord Krsna with His blackish bodily hue. Because the king of the elephants, Gajendra, thought himself an ordinary animal, he thought himself unfit to see the Lord. In his humility, he thought that he could not practice yoga. In other words, how can those who are like animals in the bodily concept of life, and who have no purity of consciousness, practice yoga? In the present day, people who have no control over their senses, who have no understanding of philosophy and who do not follow religious principles or rules and regulations are nonetheless pretending to be yogis. This is the greatest anomaly in the practice of mystic yoga.

From Srila Prabhupada’s purport to SB 8.3.28