Festive warmth is in the air. Indian communities all over the world are gearing up for the big Diwali celebrations. Their enthusiasm can be felt with lights, hues and the spirit of traditional fervour. Festivities start with Dhanteras which is celebrated all over the world today by the Indians. While a lot of us associate Dhanteras with wealth and an occasion for the purchase of precious metal, jewellery and utensils, there is more to Dhanteras.  
Dhanteras is usually celebrated on triodashi of the Krishna Paksha(the propitious 13th lunar day of the Krishna Paksha of the month of Karthik). Dhanteras word comes from Dhan(wealth) and Teras(thirteenth). 

Origin
According to one legend, Dhanteras is the birthday of Dhanvantari, the god of good health and originator of Ayurveda. According to Puranas, he emerged from the ocean of milk(Amrit or divine nectar) when the galaxy was churned during the battle between the Devas and the Asuras
Dhanteras marks the beginning of the five-day celebration leading up to Diwali. It is marked by worshipping Lord of Wealth, Kuber and Goddess Lakshmi and prayers are made for prosperity and general wealth. 
Homes are cleaned and decorated with lights and colourful Rangoli designs to welcome the Goddess. It is especially thought to be an auspicious day to buy gold, silver articles, jewellery, utensils or kitchenware as this is considered to bring good luck and well being. In the evening, Lakshmi Puja is performed in the traditional way by lighting up diyas, offering sweets to the Goddess, singing devotional hymns(Aartis) and performing rituals. Diyas are to be kept burning all through the night. In villages, farmers also adorn and worship their cattle.
Businesses decorate their premises, design the entrance with Rangoli motifs, flowers, vermilion powder and lights. 

The following things are considered auspicious to buy on Dhanteras:

  • Metal Utensils
  • Ganesh-Lakshmi Idol
  • Broom
  • Salt
  • Rudraksha
  • Gold/Silver
  • Accounting books/register
  • Swastik symbol

Things NOT to buy:

  • Iron or steel(since it is another form of iron)
  • Sharp objects like knife or scissors
  • Glass products
  • Black objects

How to celebrate Dhanteras(courtesy Quora.com):

  1. Get up early in the morning, and after your daily puja & sandhya vandana etc, clean the house, prepare a rangoli in front of the house.
  2. Put a lamp (diya) of Til Oil in the middle of rangoli.
  3. Take a Lota (a small jug like vessel) with water, put some flowers in it and hold it close to your chest in both the hands. Invoke all the tirths (Ganga, Yamuna etc) in that vessel, and then facing south pray to Lord Yama. Thank him for taking care of your ancestors, permitting them to visit us here, for coming all the way to take them back to the Pitra Loka, for the opportunity he is giving us to live here, and pray for his blessings for the strength & wisdom to live a righteous life like him, and also to ultimately understand the great discourse he gave to Nachiketas about the secrets of our self & life, much before he comes to finally take us to the realms beyond. Thereafter stretching both the hands pour this water in that direction (south), and do namaskar.
  4. Fill up the Lota once again, put some flowers in it, and face east. Now pray to your forefathers. Thank them for their boundless love & concern for us. Thank them for their regular personal visits to our loka, pray for their blessings so that we make the best of our lives, and continue the great tradition of caring for our young ones. May we too live a life by which our people may be proud of us. May we have the strength & wisdom to continue such great & noble traditions, and may we resolve that such loving & caring traditions do not stop with me. Pour the water in front of you with both hands stretched. While our ancestors should always remain source of inspiration & role models for us, and thus always reside in our hearts, yet request them to visit you all again in the coming year.
  5. Fill the vessel again with water, and now face north and pray to all the Rishis, and do a special namaskar to Sage Dhanvantari, who had manifested on this day to bestow us the wisdom of Ayurveda. Pray to Sage Dhanvantari that may we always have good health, die with our boots on, and whenever required & necessary, resort to natural ways of treatment. Thank all the Rishis for all the profound wisdom they have given to us, and pray for their blessings so that we understand their vision, and assimilate all the values which they have so compassionately expounded. May good health and knowledge - whether worldly or of things beyond, always remain our foremost priority. Pour the water in the similar manner in the north direction, and do namaskar to all the Rishis, and a special namaskar to Sage Dhanvantari.
  6. Feed food to some deserving & needy people.
  7. Buy some new utensil, ornament or equipment on this day with the resolve that may you continue the good work of supporting & feeding all deserving & needy people.