Hello there! Here are some ways a writer can describe about two characters to help develop their personalities:
- Through their thoughts and actions: How they react to or what they think after certain situations can show if they're sympathetic, jealous, rude, stuff like that, basically their traits.
- Hobbies/Interests: What they do for fun can tell a lot about them. For example, a serial killer and ballerina are, well, very different. Showing what they do reveals them more as a person.
- How they present themselves: this can show a lot about a person, especially with how they take care of themselves, if they shower often, how they walk...
- How they interact with other characters: You know the cliche grumpy old neighbor - or the snobby popular girl? These cliches are built up from how these characters interact with others. A snobby girl could talk down on people she believes are not as good as her. the grumpy man may yell at kids for crossing his lawn
These are all factors you can take into account. In summary, how characters interact with their environment, society and themselves really goes to show their personalities. I hope my answer was helpful, have a great day!