Chai is the national drink of India, commonly made with a strong black tea and Indian spices. This tea may be drunk as is but the addition of milk and sugar brings out all the wonderful flavors.
As a guideline we recommend brewing the tea first, nice and strong. Add hot milk at a ratio 7/8 tea with 1/8 milk, although you may like more milk, this is a guideline! Whole milk brings out the richness of the flavors best. White sugar is the better sweetener for chai, to get the fullest flavor from the spices without introducing a new flavor.
And one last note: Chai means tea in India. So when ordering just ask for a chai, not a chai tea or you will be ordering tea-tea!