Well, in this kind of fanfiction, the relationship between Jack Frost and the original character (OC) can be really diverse. It could be a friendship where they start off as strangers and gradually become close pals, perhaps sharing their unique powers and experiences. For example, the OC might have a special power related to nature, and they team up with Jack Frost to protect the world from some dark force.
The main characters are obviously Jack Frost and the Guardians. The Guardians typically include characters like North (Santa Claus), Tooth (the Tooth Fairy), Bunny (the Easter Bunny), and Sandy (the Sandman).
A good one often has well - developed characters. For Jack Frost, his transition from his normal form to human (if that's the plot) should be believable. The writer should capture his essence, like his mischievousness and his connection to winter. Also, the story should have a solid plot. Maybe it's about Jack Frost experiencing human emotions for the first time and how he copes with them. Good grammar and spelling are also important as they make the reading experience smooth.
Another plotline could be the OC being in danger, and Jack Frost having to rescue them. This could be because the OC has a special power that some evil force wants to steal or because the OC has accidentally stumbled into a dangerous situation while exploring the magical world. Jack Frost then uses his ice powers and his wits to save the OC and keep them safe.
One possible plot could be that Jack Frost is corrupted by a dark force. He starts to spread winter not as a fun, playful season but as a harsh, unforgiving one. He might turn against the other Guardians, believing they are holding him back from his true power.
One idea could be that Jack Frost discovers a new hidden power within himself while interacting with the Guardians. This power could be related to an ancient magic that the Guardians didn't know about. Another plot could involve Jack Frost having to prove himself to a skeptical Guardian who doesn't believe he's worthy of being part of the group. And a third plot idea might be that Jack Frost and the Guardians team up to face a new and powerful enemy that threatens the balance of the world they protect.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). There are often a lot of filters you can use to narrow down the search specifically for Jack Frost human fanfiction in the 'Rise of the Guardians' fandom. Another option is FanFiction.net, which has a large collection as well. Some Tumblr blogs also curate and share great fanfiction, so searching relevant tags there might be fruitful.
Pitch Black would be a likely main antagonist. He could manipulate Jack Frost into turning dark, as he has a history of preying on the insecurities of the Guardians.
Jack Frost is often depicted as a magical winter spirit who brings cold and frost. He's known for his mischievous nature and the ability to create winter wonderlands.