A Vrat (fast or Vow) taken thinking of Vishnu in mind.

Worship after bathing his image on the first day of the vow of the four days, beginning with the second day of the Poonam of Poush month with mustard; on the next day with gingelly seeds, on the third day with Orris root and on the fourth day with medicinal herbs. After bathing the image as given above, worship him as Krishna, on the second by the name Acyuta, and on the third day by the name of the Ananta and on the fourth day, by the name Hrsikesa.

Offering flowers at the feet on the first day of the lord should perform the worship. On the second day on the navel. On the eyes on the third day. On the fourth day on the head.

The moon should be worshipped by the names such as Sasi on the first day. Chandra on the second day. Sasanka on the third day. Indu on the fourth day. As mentioned in the Agni Purana. This is the worship of Vishnu vrat done by the kings, women and Devas (gods)

Here's some nectar on Srimati Tulasi Devi

Karttikeya once asked his father, Lord Siva, " My dear father, which tree or plant is capable of giving love of God?"

Lord Siva replied, ‘ My dear son, of all trees and plants, Tulasi Devi is the topmost; She is all auspicious, the fulfiller of all desires, completely pure, most dear to Lord Krishna, and the topmost devotee.’ Long ago, Lord Krishna, for the welfare of all conditioned souls brought Vrinda Devi in Her form of a plant, [Tulasi] and planted Her in the material world. Tulasi is the essence of all devotional activities. Without Tulasi leaves, Lord Krishna does not like to accept Flowers, foodstuffs, sandalwood paste; in fact, anything without Tulasi leaves is not looked upon by Lord Krishna. One who worships Lord Krishna daily with Tulasi leaves attains the results of all kinds of austerities, charities and fire sacrifices. In fact, he does not have any other duties to perform, and he has realized the essence of all scriptures. Just as the Ganges River is purifying all who bathe in her, so Tulasi Devi is purifying the three worlds.

It is not possible to describe the full benefit of offering Tulasi Manjaris [flowers] to Lord Krishna. Lord Krishna, along with all the other demigods, lives wherever there is Tulasi Devi. For this reason, one should plant Tulasi

Devi in one's home and offer worship daily. One who sits near Tulasi Devi, and chants or recites prayers will attain the results much faster. There are two verses from the Skanda Purana, one of which is, 'Tulasi is auspicious in all respects. Simply by seeing, simply by touching, simply by remembering, simply by praying, simply by bowing before, simply by hearing about, or simply by sowing the tree, there is always auspiciousness. Anyone who comes in touch with the Tulasi tree in the above mentioned ways lives eternally in the Vaikuntha world.

So from this verse we can understand how pure if the service which Tulasi offers to Sri Krishna. So we should always endeavor after becoming a servant of Tulasi Devi. Tulasi Devi never goes back to Godhead; she is always with Godhead. She is a pure devotee and thus she has appeared on this planet to render service to Krishna by being offered in all Temples throughout the world by being offered up to the lotus feet of Krishna.

So in this way, we can see that the worship of Tulasi Devi is actually very purifying and will definitely benefit us on our spiritual path. Even if we are not worshipping Deities, or we are unable to have an altar, the presence of Tulasi Devi is good enough.