I am posting the legend and ritual behind celebrating this auspicious day which I found on this link :
Keralites celebrate their New Year on the first day of the Malayalam month of Medam according to the Kollam calendar. This usually falls on 14 April. A festival of gaiety and renewal, this day is celebrated with great fun in Kerala.
The Kollam era is said to have begun on the day Parashurama, the sixth incarnation of Vishnu, created Kerala by making the waters of the Arabian Sea recede. Parashurama had vowed to exterminate the Kshatriya caste from the face of the earth. In keeping with this oath, he went to war with Rama, who was a Kshatriya.
During the battle, he realised that Rama was none other than the seventh incarnation of Vishnu. He realised that the purpose of his own life had come to an end and decided to spend the rest of his life in meditation. For this, he wanted a place where he could meditate in total peace. The gods granted him a boon according to which, he was to throw his battle axe into the sea and land would rise along the distance it covered. This is how Kerala was created.
The main ritual on this day is Vishukkani and Vishu Kaineettam . It is believed that the first objects which one sees on the morning of Vishu determine the prosperity experienced in the coming year.
As a result, people make it a point to see all the auspicious things as soon as they wake up. This is called Vishukkani . A special ritual arrangement of auspicious articles like rice grains, fresh linen, golden cucumber, betel leaves, arecanut, metal mirror, yellow flowers, a holy text and coins is made in a bell metal vessel called uruli . A bell metal lamp called nilavilakku is lighted near it.
When the day begins, people behold this ritualistic arrangement. A puja is performed and sweets offered to the gods. Older members of the family give kaineettam (token amount of money) to the youngsters, as part of the celebrations. The Kanippoo (flower of cassia) is considered especially auspicious for both the kani and puja on this day.
Hope you all have a vishu filled with happiness and blessing from the lord !!