In a 'Jon Snow sits on the Iron Throne' fanfiction, Jon might start by reforming the way the throne is perceived. Instead of it being a symbol of power and fear, he could make it a symbol of unity. He would have to make tough decisions regarding the remaining White Walkers threats, if any. Also, his relationships with other characters like Daenerys' followers would be very interesting to explore as he tries to bring stability to the Seven Kingdoms.
His half - sister Sansa would likely be one of his allies. She has proven herself to be a shrewd politician and would be a great asset in ruling the Seven Kingdoms. Also, the North would most probably stand by him, considering he is a Stark.
A great deal of Jon Snow and Iron Throne fanfictions focus on his relationships. For example, his relationship with Daenerys could be very different in fanfictions. In some, they rule together on the Iron Throne, combining their claims and powers. In others, they are at odds, with their relationship being a major obstacle in Jon's path to the throne. And of course, there are fanfictions where his Stark family ties also influence his actions regarding the Iron Throne, as loyalty to his family is a strong part of his character.
The North would surely support him. They have always seen him as one of their own and a great leader. Also, the wildlings might back him, considering he has a history of working with them and understanding their plight. Davos Seaworth would most likely be on his side as well, given his loyalty to Jon in the past.
One ending could be that Jon Snow ascends the Iron Throne alone. He has proven himself as a leader, defeated his enemies, and is seen as the rightful king. This ending might show him ruling with justice and mercy, much like how he was in the original series. Another ending could be that he refuses the throne. After all the chaos and bloodshed, he realizes that power is not what he wants and instead chooses to go back to the Wall or live a simple life in the North.
Well, in a 'Jon Snow takes the Iron Throne' fanfiction, perhaps Jon discovers some long - lost magic or prophecy that gives him an undeniable claim to the throne. He has to fight off some last - ditch attempts by his enemies to stop him. Once on the throne, he might start a new era of peace by making alliances with former foes. He could also start to rebuild the parts of Westeros that were destroyed during the wars, using the resources and manpower available to him in a smart way.
One common theme is the struggle for power. Jon has to face those who oppose his claim to the throne. Another theme is identity. Discovering he is the heir makes him question who he really is.
Well, it really depends on what you're looking for. There are fanfictions that focus on the political intrigue that follows when Jon's claim is revealed. Others might be more about his relationships with other characters in the context of being the heir. I'd recommend searching on platforms that have a large Game of Thrones fanfiction community and reading the reviews to find the good ones.
In a fanfic where Jon takes the Iron Throne, it could bring a new era of leadership. Jon has always been a character with a strong sense of justice. He might use his position to unite the Seven Kingdoms in a more equal way, focusing on the needs of the common people rather than the power games of the nobles. He could also be more lenient towards the North, given his roots there, and perhaps make it a more independent part of the realm while still being part of the overall kingdom.
Their relationship could become strained as they face the challenges of ruling. They might have different ideas on how to govern Westeros, which could lead to arguments.