As is the case with other systems of belief, people may think of themselves as Buddhist having been born into a family of Buddhists, or into a culture where Buddhism is predominant, and may never actually go through any ritual.
It is not necessary to give up any religious affiliation to practice Buddhism unless that religion demands actions that contradict Buddhist principles. Also, it is not generally necessary to change one's habits of diet, dress or relations with others, though some people choose to do so. Khenpo Karthar Rinpoche says that giving up other spiritual practices is not necessary to become a Buddhist. He says, "Just because you make a new friend, you don't have to give up your old friend."
The procedure by which one makes the choice to become a committed Buddhist however, is known as Taking Refuge. We take shelter in the protection and guidance of The Three Jewels: Buddha, Dharma and Sangha. Many people say that they experience a real sense of relief on the occasion of taking Refuge, as if they have really come in out of a storm to a place of warmth and comfort.
To prepare for the ritual, people generally bathe to feel fresh and to symbolically wash away the past. It is a traditional thing to do in many different cultures, and it helps create a feeling of purification and rebirth. Some people, knowing about the hair-cutting tradition, might arrange their hair so that the symbolic gesture of the Buddha's representative will be easy. In keeping with the aspect of renunciation, avoid the wearing of perfumes and other scented products. Also, strong odours can be distracting, even annoying, to people around you. People sometimes put on new or festive clothing. There is no requirement except to dress modestly and comfortably.
Take into consideration that the ritual postures can expose more than is appropriate, and that celibate people may be present. (We might think nothing of wearing shorts, sleeveless / form-fitting tops, hip-hugging pants that reveal too much especially when the person is seated and so on, but other people, certainly those of the older generation, may feel uncomfortable.)