Basically I just mix black tea, spices and brown sugar and infuse some warm milk. I like to make up a large mixture of the spice and keep it in a jar so it's quick and easy to make when I fancy a chai.
To make 4 mugs I would suggest trying the contents of 4 tea bags of black tea (throw the actual bags away), 1 tbsp soft brown sugar, 20 whole cardamom (slightly crushed), 20 whole cloves, 2-3 sticks of cinnamon, 10 black pepper corns. You can then adjust the spices to your taste. This can then be stored in a air tight jar.
When you wish to make up the drink place the spice mix in a saucepan along with 4 mugs of milk. Bring it slowly to the boil on a low heat and simmer for a few minutes, stirring occasionally. Turn off the pan and leave to infuse for a few minutes before straining into mugs. Yum!