In the finale of ATLA, Aang chooses to contact some of the past Avatars for advice on what to do with Ozai. They all give him advice with the clear recommendation that Aang should kill Ozai. Something I noticed was that Aang technically follows their advice, but ends up not killing Ozai, and therefore, they truly did help Aang reach a decision defeat the Firelord.

Roku: "You must be decisive." Roku's is short and simple, but Aang clearly follows it. He makes the decision to not kill Ozai and instead take his bending away. In addition, Aang intentionally stops the Avatar state that would have killed Ozai and gives up that power and clear advantage he had.

Kyoshi: "Only justice will bring peace." Kyoshi obviously meant that Justice = Killing Ozai but Aang brings about justice a different way. It's very arguable that taking away Ozai's power and putting him in prison forever is a much more significant karmic justice that death could never bring.

Kuruk: "You must actively shape your own destiny." This is a line that Iroh would use a lot and is basically one of the big points of Zuko's character, but it applies to Aang too. Everyone, these past Avatars and even Aang's friends like Zuko and Sokka kept telling Aang that he must kill Ozai; there is no other way. Aang basically said screw that and sought out to find a different way (through the help of the lion turtle). This draws another parallel to something Iroh said to Zuko: Aang followed his own destiny, not a destiny someone tried to force on him.

Yangchen: "Sacrifice your own spiritual needs, and do whatever it takes to save the world." This one is a bit trickier, as Aang technically doesn't sacrifice his spiritual needs. He is able to save the world and keep his morals and character. However, he certainly does "whatever it takes" to save the world. By choosing to find a different means to defeat Ozai, it shows that he took the hard way to complete his goal. He could have very easily killed Ozai in the Avatar State. Basically nothing would really change and no one would look down on him for it. However, Aang decides that it not an option, and so a non-lethal strategy is "what it takes" to stop Ozai.

In summary, Aang takes the advice of the Avatars to do one thing, but ends up doing something completely different while still following their advice. Whether Aang was actively aware of it or not, the Avatars were a major help in the decision Aang made and the conclusion of the series.

These points might be obvious to some people, but it was just something I was thinking about. I thought it was neat so I figured I'd write it down.