One possible plot twist could be that Jon Snow goes back in time and accidentally changes something that leads to a completely different future for the Stark family. For example, he might prevent Ned Stark from going to King's Landing, which would change the power dynamics in Westeros entirely.
His relationship with his father, Ned Stark, would be different. He could finally have a real father - son relationship instead of the hidden one. He might be able to learn from Ned and become an even better leader in the North.
Regarding his relationships with his friends and comrades, like Samwell Tarly, things would be altered. He might not meet Sam in the same way as before. And his relationship with Daenerys Targaryen could be completely different. Instead of meeting her during the events of the original story, he could meet her when she was much younger, and this could lead to a very different kind of relationship, maybe one that's more of a mentorship or a completely different romantic connection.
One common theme is redemption. Jon often goes back to correct past mistakes, seeking to atone for things he did wrong in the original timeline. Another theme is the butterfly effect. His actions in the past can have unexpected and far - reaching consequences in the future.
The wildlings might be his allies. After all, Jon Snow has had interactions with them before. They are fierce fighters and could fight alongside him against a common enemy.
He could meet ancient Valyrian dragonlords. These dragonlords might still have some connection to their dragons, even if the dragons are long gone or in hiding. Another possibility is meeting the descendants of the original Valyrian slaves who have their own unique stories and skills.
One popular 'jon goes back in time fanfiction' might be 'Jon's Time - Travel Adventure'. In this story, Jon goes back to a crucial moment in history and has to figure out how to change certain events without causing too much chaos. Another could be 'Jon's Journey Through Time', where he meets important historical figures and learns valuable lessons from them.
In this fanfiction, perhaps Jon Snow goes to Valyria to discover ancient secrets about his heritage. Maybe he finds lost Valyrian steel - making techniques or uncovers hidden knowledge about the White Walkers' origin. It could also be that he meets some long - lost relatives or discovers a new power source there.
Well, it could be about Jon Snow leading his men into a great battle against the White Walkers. Maybe he discovers new strategies or forms unexpected alliances during the war.
In some fanfictions, if Jon Snow goes to Old Valyria, he may meet characters from the past. He could interact with ancient Valyrian families or even those who were involved in the events that led to the Doom. This could give him insights into the history of the world and how it has shaped the present, and potentially give him ideas on how to deal with the threats in Westeros.