Hermione was a prominent example of this as, on the surface, she appeared like someone who would fit right into Ravenclaw. But beyond her interests, her values define her as someone with a take-charge personality and bravery to spare. Unlike Ravenclaws, she didn't apply knowledge in unique ways.
Hermione isn't creative enough to enjoy or appreciate Divination as a discipline, whereas a Ravenclaw might be more open-minded. Hermione values bravery and friendship over books and cleverness. While Hermione is known as the smartest witch of her age, her intelligence isn't what she values the most.
It was confirmed on Pottermore that Hermione was also a bit of a Hatstall, as the Sorting Hat saw the potential for her to be both Ravenclaw and Gryffindor. In the end, Gryffindor won out, and it's possible that Hermione wanted to be seen for being brave more than for her intelligence.
Hermione wasn't in Ravenclaw because she valued bravery over intelligence and curiosity. She says so herself many times. One of the first things she says to Ron and Harry is “Do either of you know what house you'll be in?
Ron Weasley
Being Harry Potter's best friend certainly needed heaps of bravery – hence the Sorting Hat not messing around in sorting Ron into Gryffindor, the house of his parents, brothers and sister.
He actually asked the Sorting Hat to place him in Hufflepuff, as he was intimidated by Gryffindor's reputation for bravery, but the Sorting Hat didn't agree. They debated it for so long, that he was close to being what is known as a Hatstall, which is a term for any student whose Sorting takes longer than five minutes.
As others have mentioned Harry is ambitious and wants to prove himself which are the traits of a Slytherin but the main reason was that he had a part of Voldemort's soul in him and that's why hat had troubles sorting him.
J.K. Rowling also branded Ravenclaws as “the most individual” (take that other houses!). Along with this, Ravenclaws are eccentric and creative. Perhaps the most recognizable Ravenclaw in the Harry Potter series, Luna Lovegood is certainly eccentric.
Despite being overlooked and often mocked by her peers, she never once doubts herself. She has the strength to believe in herself and her own wisdom – a trait which makes Luna Lovegood a true Ravenclaw.
Her real parents were Daneel and Dean Novak, Pureblooded wizards. Turns out Daneel was Tom Riddles younger sister, Daneel Riddle. Of course, the Riddles were related to Salzar Slytherin himself, and this made Hermione the living heir of Slytherin.
The point is that I think Luna embodies the very best characteristics of Ravenclaws: she's inquisitive, never satisfied with just a little bit of knowledge, and she's drawn to mysteries and the unknown.
He was a Gryffindor
Hagrid's Hogwarts house is never mentioned in the books, but, given his kindness, noble nature and bravery, it might not come as that much of a surprise that Hagrid was in Gryffindor.
Ginny is a pureblood witch born 11 August 1981, the seventh child and only daughter of Arthur and Molly Weasley. She attends Hogwarts School of Witchcraft and Wizardry, and is sorted into Gryffindor house, along with the rest of her family.
For Albus no matter what house he was placed in he would have to deal with his father's reputation. Albus made a friend who was in Slytherin, so he wanted to be in Slytherin. The hat took pity on him and allowed him to be with his friend. I think the same thing happen the Sirius when he was chosen into Gryffindor.
She is perceptive
Ravenclaws are perceptive, and Luna noticed all kinds of things others didn't during her time at Hogwarts.
Her motivations and values are not Slytherin in nature. While she does possess pretty much all Slytherin traits she does not value them like she values her Gryffindor traits. She thinks it's important and admirable to be brave, but not ambitous. And her motivations are of a generally selfless nature.
Moaning Myrtle
Born in the late 1920s to Muggle parents, Myrtle Warren started her Hogwarts life in the early 1940s, where she was sorted into Ravenclaw.
1 Rowena Ravenclaw
As one of the most famous Ravenclaws, Rowena built her house on the ideals she valued and embodied — intelligence and creativity.
Who were the heirs of each of the four founders of Hogwarts? Ravenclaw heir is the Grey Lady; aka Helena Ravenclaw. We do not know if she has any other children or if Helena had any children. So we don't know if there are any Ravenclaw heirs alive at the time of Harry's hogwarts days.
Slytherins in love
Look at Lucius and Narcissa – a total power couple. After a fellow Slytherin, the next best match for this shrewd house would probably be Ravenclaw. A Slytherin could use Ravenclaw's intellectual and inquisitive nature to their advantage, plan their world domination in minute detail.
Severus was Sorted into Ravenclaw, thankfully avoiding being sorted into Slytherin, as that would put a strain on his relationship with his best friend and true love, Lily Evans. While attending Hogwarts, it was noticed since his first day that the boy was a prodigy.
ENEMIES. Slytherins and Ravenclaws - Slytherins hate rules and Ravenclaws are ingenious. Together they can take over the world or create amazing spells. Or they can hate eachother with a fury and rage.
But when they went to Hogwarts, everything changed. The pair were parted when the Sorting Hat placed Severus in Slytherin and Lily in Gryffindor, and while Lily thrived in her new, magical life, Snape was essentially placed in close quarters with the likes of Lucius Malfoy, Avery and Mulciber.
Being scarred by his past experience with Tom Riddle, Dumbledore would have taken heightened precautions to prevent Harry from traversing down a similar slope of moral disrepute. Plot-wise, having Harry be in Slytherin would have resulted in Dumbledore being much more aware of his connection to Voldemort.
6 Peter Pettigrew: Slytherin
This example is one of the most obvious Sorting Hat mistakes that is talked about in the book. The Sorting Hat took more than five minutes to put Peter Pettigrew into Gryffindor.