There are certain trends by which people often choose their characters' houses. Unfortunately, these often demonstrate a widespread misunderstanding of the Hogwarts houses.
It usually goes something like this:
- My character is athletic and fearless, and should be sorted into Gryffindor.
- My character is chummy and loyal, and should be sorted into Hufflepuff.
- My character is brainy and studious, and should be sorted into Ravenclaw.
- My character is conniving and selfish, and should be sorted into Slytherin.
This can be a superficial way to see the houses, and often leads to highly inappropriate sortings. If this is all there were to it, then Ron Weasley would have been a Hufflepuff, and Hermione Granger would undoubtedly have been a Ravenclaw. But the Sorting Hat looks much deeper than this, into the core of a person's being. It saw that Ron and Hermione both belonged in Gryffindor. But why?
A much clearer lens to look through is to ask yourself: How does my character approach problems?
- Gryffindors solve problems with bold action driven by emotion and a sense of righteousness.
- Hufflepuffs solve problems with perseverance and cooperation.
- Ravenclaws solve problems with thoughtful consideration and careful planning.
- Slytherins solve problems with cunning, looking for opportunities to use the situation to advance their own position.
(Naturally, there are also blood status considerations with Slytherin. Those that behave like Slytherins, but don't have the blood for it, are most likely going to end up in Ravenclaw.)
To use the above examples from the books, both Ron and Hermione act like Gryffindors. Sure, Ron is a faithful comrade, and Hermione is the smartest girl at school, but it's not what is on the surface that matters. How they approach things says far more about their natures. The typically cautious and rational Hermione regularly broke the rules and simply did what needed to be done, even in the face of danger. That's a Gryffindor all the way. One could argue that Crabbe and Goyle had the trappings of Hufflepuffs, given their devotion to Draco Malfoy. However, when it came down to it, they attached themselves to Draco not out of loyalty, but because he was their only real hope of advancing themselves.
Obviously, there are more than four ways to handle problems. But odds are, any given character will fit one of these methods more so than the other three.