Well, he might use simple distractions. For example, he could create a minor commotion to draw attention away when he's about to use a particular skill subtly. Maybe he pretends to be clumsy or make a small mistake on purpose so that others don't suspect he has advanced skills.
He could also be very careful with his chakra control. By suppressing the outward signs of chakra flow when using his skills, it would be harder for others to detect. He might practice in secret and only use his skills when absolutely necessary, like in a life - or - death situation where he has no other choice but to show a bit of what he can do without fully revealing all his capabilities.
Perhaps Naruto is waiting for the right moment to reveal his skills for maximum impact. He could be planning a big surprise for his enemies or wants to make a grand entrance at a crucial time. For example, in a major battle against a powerful foe, he could suddenly unleash all his hidden skills and turn the tide of the battle, which would be more effective than showing them off gradually.
Maybe he wants to protect his loved ones. If his enemies know his true strength, they might target his friends and family to get to him. So, by hiding his skills, he can keep them out of harm's way while still being able to fight when necessary.
Maybe he wants to surprise his opponents in battles. He could be waiting for the perfect moment to reveal his full power and turn the tables on his enemies.
Perhaps he has hidden the full extent of his Sage Mode abilities. He might be able to stay in Sage Mode for a much longer time than he has shown so far, or have some other undisclosed powers within that mode, like the ability to sense enemies from much greater distances.
Another possibility is that Naruto has a plan that requires him to keep his skills hidden from everyone, including Hinata, for a while. He could be waiting for the right moment to reveal them and use them to surprise and save the day, especially when it comes to protecting Hinata from a big threat that he anticipates.
Another reason could be related to his personal growth. He might be trying to master the power of the eye in private. Naruto has always been one to face challenges alone at first. By hiding his eye, he can focus on understanding and using its power without distractions or the pressure of others' expectations.
Well, Naruto hiding his skills can add a lot of suspense to the plot. It makes the other characters underestimate him at first. For example, his opponents might think he's an easy target, but then he reveals his true abilities at crucial moments, turning the tide of battles or situations. This creates exciting twists in the story.
Well, she could start by dressing in a more androgynous way. Maybe wearing loose-fitting clothes that don't give away her feminine shape. Also, she might try to lower her voice or use certain speech patterns that are more associated with males in that fictional world.
She might want to prove herself in a male - dominated ninja world. If she shows herself as female, she could face discrimination or be underestimated. So, hiding her gender gives her a chance to be seen as an equal to male ninjas.
He could practice in secret locations where no one can see him. For example, in an abandoned cave or a hidden part of the forest. That way, no one will know about the new jutsu he's developing.