Personally, I enjoy character research. It’s an excuse to people watch. Every new person I meet is fodder for a character.
I think people watching offers a great window into understanding character interactions. Among other things, It can help with:
Some of my favorite places for people watching are parks, coffeehouses, parties, and bars. (This may say more about the places I frequent than the people I’m watching!)
Passersby offer a glimpse into their lives. Focus on small gestures. How does someone hold his/her arms when defensive, excited? Do all joggers run with the same stride/gait? How do people laugh? How closely do they talk?
I also love to imagine what people are talking about, making up conversations for them (some times only for my own amusement). Do you notice how people say words like “especially, probably, interesting.” How is spoken grammar different from written?
The important part is not pulling out only the quirky, exciting details of a person but showing the reader why s/he behaves that way. In other words, once you find an interesting trait, the fun has only just begun. Explain why the character has this trait…a posture, a way of running, a certain set to his/her chin. You can uncover a whole new dimension to your character simply by adding a trait from real-world observation.
Enjoy your research!