Iron Man could be a visiting alien from a far - off galaxy that has advanced technology similar to his suit. He could land on a planet like Tatooine and get involved in local disputes. Maybe he helps a moisture farmer against a group of Tusken Raiders using his repulsors.
The 'unlikely alliance' trope is also common. For example, Iron Man teaming up with Darth Vader before Vader's full turn to the dark side. They might work together on a project that could change the fate of the galaxy. And then there's the 'culture clash' trope, with Stark's modern Earth values clashing with the values in the Star Wars universe.
It would be amazing. Just imagine Iron Man's high - tech suit in the Star Wars universe. He could be a lone bounty hunter with his advanced weaponry, or perhaps he teams up with the Rebels and uses his technology to upgrade their ships. His suit's repulsors would be a new and powerful addition to the Star Wars combat scenarios.
In fanfiction, Iron Man could fit into the Star Wars universe in many ways. One way is that he could be a time - traveler of sorts. He arrives in the Star Wars era and decides to use his technology to make a name for himself. He could start his own faction, using his Iron Man suits as his army. His suits could be modified to blend in with the Star Wars aesthetic. He'd have to learn about the Force and how it affects the balance of power, and his relationships with the various species and characters would be a major part of the story.
One interesting crossover could be Iron Man's technology being introduced into the Star Wars universe. Maybe he could help upgrade the droids or the starships with his advanced engineering skills. Another could be a scenario where Tony Stark finds himself in the middle of a lightsaber duel, using his suit's capabilities to fend off the Jedi or Sith.
Another popular character is Chewbacca. Picture Chewbacca and Iron Man in the same scene. Iron Man might be initially confused by this large, furry alien, but then they could end up working together. Maybe Chewbacca helps Iron Man understand some of the more wild aspects of the Star Wars universe while Iron Man uses his tech to solve problems for Chewbacca's friends.
One good example could be a fanfiction where Tony Stark's secret identity is at risk when a new villain has some sort of technology that can detect his hidden identity. In this story, Pepper Potts might play a crucial role in protecting his secret, perhaps by creating false leads or using her business connections to throw the villain off track. Another example could be a fanfiction set in an alternate universe where Tony's secret identity is known only to a select few, like Rhodey and Happy, and they have to deal with the consequences of a leak within this small group.