One common strategy is deception. Harry could pretend to be compliant with the Ministry's rules while actually going against them. For example, if the Ministry is trying to restrict certain magical activities, Harry might do them in secret and make it seem like he's not involved.
In some fanfictions, Harry might use his knowledge of magic that the Ministry doesn't expect. For example, he could use ancient spells or charms he learned from old books. He may also outsmart the Ministry by using his friends' skills cleverly. If Hermione has some special knowledge about Ministry regulations, Harry could use that to his advantage.
One interesting strategy could be his use of misdirection. He might make others think he's going one way while actually doing something completely different. This keeps his opponents guessing.
It can be. Fanfiction often subverts the traditional power dynamics. Harry, having grown up in a different environment than Dumbledore, might have a different perspective on magic. He could use his street - smart nature, gained from his years with the Dursleys, combined with his magical knowledge to come up with solutions that Dumbledore wouldn't think of. Also, his bond with his friends could give him an advantage in certain situations where Dumbledore might act more alone.
In some fanfictions, Harry might use his knowledge of magic in unexpected ways. For example, he could combine spells in a new and creative manner that others haven't thought of. This gives him an edge over everyone.
In some fanfictions, Harry might outsmart Umbridge by using his knowledge of magic in unexpected ways. For example, he could use spells that are not commonly known to get around her rules. Maybe he uses a charm to make her quill write false reports, thus confusing her when she tries to use those reports against him.
A common plot device is misdirection. Harry might create a false lead or distraction that makes Snape focus on the wrong thing. For example, he could stage a minor 'accident' in the corridor that draws Snape's attention while he slips away to do something else he's not supposed to. Another device is using his friends' unique abilities. If Hermione has found a loophole in a rule, Harry can use that knowledge to outmaneuver Snape who is always strict about the rules.
Well, in many fanfictions, Harry might use his quick thinking and knowledge of magic. For example, he could use spells in unexpected ways to get around Fudge's plans. Maybe he uses a charm to make Fudge misinterpret a situation or forget an important detail. Harry is known for his resourcefulness, and against Fudge, he could use his skills to expose Fudge's wrongdoings or prevent Fudge from interfering in things that Harry believes are right.
Perhaps he uncovers some major corruption or inefficiency in the Ministry. So, as a result of his efforts to reform it, he is given control. For example, if he finds that the Ministry has been misusing magic for personal gains, he could lead a movement to take it over and run it in a more just way.
Hermione could be a key character. She is always by Harry's side, and her intelligence and knowledge of the wizarding laws would be invaluable in the lawsuit. She might be the one doing all the research and preparing the legal arguments for Harry.
Besides Harry, Hermione is a key character. She can research and find loopholes in the Ministry's laws and regulations. Ron is there too, providing muscle and emotional support. Neville Longbottom could also be involved. He has grown into a strong and brave wizard, and he might join Harry's cause. Additionally, Luna Lovegood with her unique perspective on magic could offer different ways of approaching the conflict with the Ministry. Some fanfictions might also include Sirius Black, if set in a timeline where he didn't die, as he has a history of opposing the Ministry's unjust actions.