The secret to making great chai is, of course, the spices (as it is with most Indian food). The fresher they are the better. Although what counts as perfect chai varies from person to person, it almost always includes whole cloves, cardamom and cinnamon, though nutmeg, ginger, and other spices are also common.
Chai is a staple drink with Indian food, and if you like chai as a tea, you'll probably love it as a milkshake. All you have to do is blend your favorite finished chai (with milk added, of course) with the ice cream of your choice. You can add honey and spices as flavorings, if you like.