I guess I've never made proper iced tea, only tea to which I added ice cubes.
But I suppose if were to make it, it would be similar to how I make cold brewed coffee (crush beans, soak in cold water over night).
With tea, do the same, soak tea bags in cold water overnight, along with some lemon or other fruit to add to the flavor. After 12-24 hour, remove tea and any fruits, and serve.