In many Tamil homes, important occasions begin with a Ganapathi Homam at dawn. Graha Pravesam commonly starts before sunrise, with the family entering carrying a lit lamp and kalasam, followed by Punyahavachanam, Vastu Shanti and boiling milk in the new kitchen.
Community practice shapes the details. Iyer families typically follow Smarta traditions, while Iyengar families follow the Sri Vaishnava tradition, and the two may differ in mantras, the prominence given to Shiva or Vishnu, and customs such as the namam or vibhuti worn. Other communities have their own practices as well.
Ancestral rites are observed carefully in many Tamil families. Tharpanam is commonly offered on Amavasya, especially Mahalaya Amavasya, and the annual Shraadham is performed on the tithi of a parent's passing. Since these rites vary by family, the purohit will usually ask about your gotra and your family's custom.