I made up a power point (because I'm having issues with movie maker) of what I thought would be a good opening. Take Uncle Iroh's speech from Bitter Work about the 4 nations except start with air-water-earth-fire.??
Here's the run down.
Air is the element of freedom. The Air Nomads detached themselves from worldly concerns and found peace and freedom (clips showing the airbenders).?? Also, they apparently had pretty good senses of humor!?? (Aang and Gyatso bending the cakes to hit the other monks).
Water is the element of change. The people of the Water Tribe are capable of adapting to many things. They have a deep sense of community and love that holds them together through anything. (Show the two water tribes)
Earth is the element of substance. The people of the Earth Kingdom are diverse and strong. They are persistent and enduring. Air is the element of freedom.?? (Lots of Earth bending and showing the different populations)
Fire is the element of power. The people of the Fire Nation have desire and will, and the energy and drive to achieve what they want. (Zhao giving a speech-war room-fire nation fleet)
The Avatar is the master of all four elements (Show the Avatars as displayed in Avatar State).?? And now the only one who can save us (cue Aang and show the map of the world)