Deepavali is referred to variedly in the Puranas and Dharma Sastras.
(1) A five day festival symbolising victory over Narakasura, worship of Mahalakshmi, victory of Vishnu over Bali and dice play and exchange of brotherly and sisterly affection. Bali Pratipada –Dhanteras.
(2) Naraka Caturdasi snanam with oil bath / apamarga twigs for those who fear Hell – Crushing of a bitter fruit called KarIt by foot - Performance of Yama tarpanam – Worshipping of Cows- Lighting of Lamp for avoidance of Naraka - Eating of 14 types of vegetables - In the evening lighting of lamps for the deities and decorating houses and public places
(3) On the evening of Caturdasi and Deepavali – lighting of firebrands in hand and show the way for the Pitrus who have come for Mahalaya back to their own worlds.
There are many other detailed practices which have been referred to in the scriptures.