According to my mom, here are the two ways to make masala chai: The first way results in a mixture that is slightly thick and sweet. This probably the more traditional way of making this tea in India. Here goes... Add the spice mixture to the water and heat. When the water boils, add the tea and a little later add sugar and milk. She suggests generous amounts of tea, milk and sugar, but I suspect you might want to vary the quantity according to your taste. Let the mixture stand for half a minute or so and remove from heat.
The other method is to let the water/spice mixture boil and add the tea after removing from heat. Cover the saucepan (oops, I guess I forgot to mention that in India, tea is usually made in a saucepan and then drained) and allow the tea to brew for a few minutes. Then add the milk and sugar.
The spices most commonly used in masala chai are - cardamom, cloves, cinnamon & black pepper (whole), in case you're interested in starting from scratch. Otherwise the Celestial Seasonings Bengal Spice herbal tea bags when mixed with any regular tea makes a fairly good cup of masala chai.
Hope this helps...