Naruto could act impulsively and make hasty decisions that seem unthoughtful. This would make others think he's not very intelligent. He might also avoid getting into deep conversations where his true intelligence could be revealed. By constantly changing the subject or making jokes, he can keep people from realizing how smart he is.
He might use simple language on purpose. For example, he could pretend to be confused about things he actually understands well. He may also make silly mistakes intentionally to give the impression that he's not as smart as he really is.
One way Naruto could hide his intelligence is by relying on his more boisterous and energetic personality. He could play up the part of the simple - minded, fun - loving ninja. He'd be the first to volunteer for physical tasks rather than intellectual ones, and when it comes to strategy discussions, he might act like he's not really following along, when in fact he has his own brilliant ideas but just doesn't want to show them yet.
He might want to protect himself. If others know how smart he is, he could become a target. Enemies might see him as a greater threat and go after him more aggressively.
He might put on a fake smile and act normal. Naruto is good at being energetic on the outside, so his family may not suspect that he's in pain.
In many fanfictions, Naruto might hide his pain by putting on a big smile. He's always been the type to try and be positive in the face of his friends. He could also distract others with his goofy antics, like making a joke or doing something silly to shift the focus away from his inner turmoil.
He could be using basic chakra control techniques to suppress his power. By constantly regulating the flow of his chakra, he can keep his true power hidden. For example, he might be using a form of internal chakra suppression similar to what some ninja use to hide their presence.
He might use some special jutsu or seals. For example, he could use a sealing technique to suppress the signs of his bloodline. This way, others wouldn't be able to detect it through normal means like sensing chakra.
Well, in fanfictions, often the plot takes a different turn. Naruto might hide from his family because there could be some sort of misunderstanding. For example, there could be false rumors about him being involved in something bad. And he might think that his family would believe those rumors without giving him a chance to explain. So, to avoid the immediate confrontation and judgment, he chooses to hide.
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.
One possible reason could be that his eyes hold a special power that he doesn't want others to discover easily. For example, it might be a new type of Sharingan or a unique ability related to his Uzumaki heritage that he needs to keep secret to protect himself or those around him.
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.
One possible reason could be that he doesn't want others to pity him. Naruto has always been a proud and strong - willed character. His scars might be a reminder of painful past experiences, and he prefers to deal with them privately rather than showing vulnerability to others.