A plotline could involve Naruto finding a hidden power within the Uchiha clan that was overlooked. He uses this power to unite the clan and make them strong enough to resist any threats. Maybe this power is related to an ancient Uchiha technique that Naruto helps to rediscover. He then uses his charisma and leadership skills to convince the Uchiha to work with the village instead of against it.
One possible plotline could be Naruto being adopted into the Uchiha clan early on. He might then learn the unique Uchiha jutsus and secrets at a young age. This could lead to him having a different relationship with Sasuke, perhaps as a brother - like figure within the clan.
One possible plot could be that Naruto discovers a hidden prophecy about the Uchiha clan's downfall long before it actually happens. He then uses his influence and his own unique abilities to prevent the events that lead to the clan's massacre. For example, he might find a way to resolve the conflict between the Uchiha and the village leadership without bloodshed.
If Naruto saved the Uchiha clan, the story of the Hidden Leaf Village would be rewritten. The history of the Uchiha's massacre would no longer be a dark stain on the village's past. The Uchiha would contribute their unique skills and abilities to the village's development. For example, their Sharingan abilities could be used for better security or in battles against common enemies. There would also be a change in the relationships between characters. People who were once enemies of the Uchiha might have to learn to work with them.
One way Naruto could save the Uchiha clan in fanfiction is by using his influence. Naruto is highly respected in the village. He could convince the village elders to re - evaluate their treatment of the Uchiha. He might show them that the Uchiha were being wrongly persecuted and that there was a way to co - exist peacefully. He could also use his power as a Jinchuuriki to protect the Uchiha from any external threats that might be a factor in their downfall.
In some fanfictions, Naruto might have an Uchiha bloodline awakening due to some unforeseen circumstances. This could lead to him developing Sharingan-like powers that are different from the norm. For example, his Sharingan could have a unique ability related to his Uzumaki chakra, creating a whole new set of jutsus and combat styles for him.
A possible plotline could be that Tayuya is captured by an evil organization, and Naruto goes on a solo mission to save her. He uses his stealth skills to infiltrate the enemy base.
Perhaps Artemis gets lost in a strange dimension that is similar to Naruto's world. Naruto discovers her there and has to protect her from the dangerous creatures in that dimension. He uses his skills and knowledge of the area to lead her to safety. Along the way, they might form an unlikely friendship or even more, depending on the nature of the fanfiction.
Danzo could be a main antagonist. He was always paranoid about the Uchiha clan's power and was involved in many of the events that led to their downfall. In a fanfiction where Naruto is trying to save the clan, Danzo would likely oppose Naruto's efforts as he sees the Uchiha as a threat to his own power and the village's stability in his own twisted way.
A plotline could involve Petunia having a change of heart due to a magical event. For instance, she might accidentally stumble upon some of Harry's magic or receive a message from the wizarding world about his importance. This could lead her to stand up against Vernon and protect Harry. She could then start to teach Harry about his mother's side of the family and the magic that runs in his veins in a more positive way than the Dursleys ever did. And perhaps she even helps him develop his magic skills secretly before he goes to Hogwarts.
For other Uchiha clan members, they could start to view Naruto in different ways. At first, they might be skeptical of him, but as he shows his strength and loyalty to the clan, they could come to accept him. This could also lead to Naruto influencing the Uchiha clan's traditional views and values, causing some of the younger members to think more openly about the clan's future and its relationship with the outside world.