Question
What are the steps for a person to take if he/she wants to convert to Hinduism?
Answer
Is it possible for anyone to convert to Hinduism?
As P. V. Kane says in History of Dharmaśāstra, Vol II Part I, there is no provision in the Hindu smṛtis and dharma śāstras for people of other faiths to convert to Hinduism because one is simply born a Hindu:
Hinduism has not been an avowedly proselytizing religion. In theory it could not be so. For about two thousand years the caste system has reigned supreme and no one can in theory be admitted to the Hindu fold who is not born in it.
A born Hindu however may lose his caste and gain it back:
A Hindu may lose caste, be excommunicated and driven out of the fold of Hinduism, if he be guilty of very serious lapses and refuses to undergo the prāyaścittas prescribed by the smṛtis.
...
When the sinner performed the prāyaścitta prescribed by the śāstras, he was to be welcomed by his relatives, who took a bath along with him in a holy river or the like and throw therein an unused jar filled with water; they were not to find fault with him and were to completely associate with him in all ways.
In practice though, people of foreign ancestry were absorbed into Hinduism but as to how this was done is not known and may also vary from person to person because there are no set rules (remember that in theory the smṛtis don't allow conversion to Hinduism):
The ancient smṛtis do not expressly prescribe any rites for bringing into the brahmanic or Hindu fold a person who or whose ancestors did not belong to it. But as Hinduism has been extremely tolerant (barring a few exceptional instances) it had a wonderful power of quiet and unobtrusive absorption. If a person, though of foreign ancestry, conformed to Hindu social usages in outward behaviour, in course of time his descendants became absorbed into the vast Hindu community.
This process has gone on for at least two thousand years. The beginnings of it are found in the Śāntiparva chap. 65 where Indra tells the Emperor Māndhātṛ to bring all foreign people like the Yavanas under brahmanical influence. The Besnagar column inscription shows that the Yona (yavana) Heliodora (Heliodorus) son of Diya (Dion) was a bhāgavata (devotee of Vāsudeva)...
In the caves at Nasik, Karle and other places many of the donors are said to have been yavanas ... Several inscriptions state that Indian kings married Huna princesses, e.g. Allaṭa of the Guhila dynasty married a Hūṇa princess named Hariyadevi ... king Yaśaḥkarṇadeva of the Kalacuri dynasty is said to have been the son of Karṇadeva and Āvalladevī, a Hūṇa princess. These and similar examples show that persons of foreign descent and their children were absorbed into the Hindu community from time to time. This absorption is illustrated in modern times by the case of Fanindra Deb v. Rajeshwar ... in which it was found that a family in Kooch Behar not originally Hindu had adopted certain Hindu usages and it was held that it had not taken over the practice of adoption. How Hindu customs and incidents persist even after conversion to Islam is strikingly shown by the Khojas and Kutchi Memons of the Bombay Presidency, who though made converts to Islam several centuries ago, were held by the courts in India to have retained the ancient Hindu Law of succession and inheritance.
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