One common theme is redemption. Jon often seeks revenge not just for the sake of it, but also to redeem himself or the honor of those he cared about. Another theme is power. He usually gains some form of power, whether it's political, magical or in terms of influence, which he uses to exact his revenge.
Well, there's this fanfiction titled 'Revenge of the Bastard'. In it, Jon Snow uses his skills and knowledge gained from his time at the Wall and beyond to take revenge on his enemies. He forms unexpected alliances and outsmarts his foes. It's really exciting to read as it combines elements of mystery, action, and of course, revenge. It gives a new perspective on Jon's character and his capabilities.
Jon Snow could potentially have allies like the Mormonts. They have always been loyal to the Starks. Maybe even some of the Dornish houses might side with him. They have their own reasons to oppose the current power structure in Westeros. And of course, his friends from the Night's Watch who left with him or believe in his cause could be his allies in this conquest. He might also gain the support of some of the maesters who see the value in his leadership for the future of Westeros.
Daenerys Targaryen could be one to help. Since she has experience with dragons, she could give Jon Snow advice on how to care for the egg and hatch it.
It could be a young and untainted Frey. Maybe a niece or a cousin of the more infamous Freys. One who has not been involved in the past atrocities committed by her family and has a more noble heart.
Daenerys Targaryen is often paired with Jon Snow in such fanfictions. Their combined power and the potential for a different kind of relationship makes it a popular choice among writers. Another character is Arya Stark. Their sibling bond can be explored in new ways when Jon is reincarnated, like Arya helping Jon with her assassin skills in a different plot line.
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.
Daenerys Targaryen is often paired with Jon Snow in these fanfictions. Their connection in the original series, along with their both being strong leaders, makes for an interesting dynamic. They could rule Westeros together in a new era of peace and prosperity after Jon's rebirth.
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.
In a great deal of fanfiction, Jon Snow is indeed considered one of the best swordsmen. His journey from a young boy in Winterfell to a hardened warrior gives him a lot of scope for development in terms of swordsmanship. He has had to fight wildlings, White Walkers, and various enemies in the Seven Kingdoms. His sword, Longclaw, also becomes an extension of himself in these stories. The way he wields it with precision and power makes him a formidable swordsman in the fanfiction world. Many authors focus on his growth as a swordsman, starting from his basic training under Ser Rodrik Cassel and later developing his own unique style through his adventures.