Since the current "if you were in charge" thread focuses on LOK, I think it'd be nice to have one for the original series. I would have done the following:
1. Aang does act jealous of Jet in "Jet."
2. Katara would be reluctant to see her dad in "Bato of the Water Tribe."
3.More Suki, and basically every other non bending fighter that isn't Sokka.
4. There would be at least one episode that fleshes out Air Nomad culture more.
5. Yue is given more personality.
6. Koh plays a bigger role.
7. We would see Iroh and Ozai interact at least once.
8. There would be an episode dedicated to Iroh's past.
9. Aang would yell at Sokka and only Sokka when Appa's stolen.