The Vishnu or Aditya rules this day, which is auspicious for religious ceremonies, the lighting of the sacred fire, and the performance of one's duties.
Shukla Dwadashi is the name for the 12th Tithi (lunar day). It's the 12th Tithi of Shuklapaksha. Its nature is Yasha Prada, which can be interpreted as "fame giver". It's good for following works: movable or fixed works; peaceful or Paushtik works, first feeding, Upanayana, marriage. Travelling, entering into new house and oil massage should be avoided. Vishnu is Devata which rules Dwadashi (according to Muhurta Chintamani and Poorva Kalamrita). Vishnu is Devata who stays for preservation, he's a divine power keeper. As per Brihat Samhita, Shukla Dwadashi is ruled by Savitar (one form of Surya, the Sun) and all actions done in respect of Savitar or Surya (health, king, governmental works, helping father etc) are acceptable during this day. Being Bhadra (that can be translated as "lucky") and ruled by Buddha (Mercury), the 12th Tithi of Shuklapaksha is suitable for following works or actions: marriage, Upanayana, ornament making and using, clothes; art; travelling by elephant or horses, travel, conveyance; making of roads; oil massage.
Dwadashi Tithis have various other religious observances through out the year. Kurma Dwadashi is dedicated to the worship of Kurma, the second Avatar of Vishnu. Govinda Dwadashi or Narasimha Dwadashi, which falls in the month of Phalguna celebrates the Narasimha Avatar of Vishnu, before Holi. Rama Lakshmana Dwadashi is important for begetting a son, who is considered as important, to Moksha or salvation; in Hinduism. King Dasharatha had observed the Rama Lakshmana Dwadashi to beget God Rama as his son. Jagannath Temple of Puri has special celebrations on this Dwadashi for Utkala Brahmins.[1] Govatsa Dwadashi is the first day of celebrations on Diwali, on which cows are worshiped as symbolic to mothers; nourishing mankind, and being the chief means of livelihood and religious sanctity in rural India.