Justin Chon gave a quick interview to J-14:

“J-14: In Twilight, did you draw from your own high school experience to flirt with Bella Swan in the cafeteria?
Justin Chon: Of course. As an actor you’re always trying to draw from real stuff to make it real, but I would say in acting terms, you use like substitutions and you think back to the moment. I just tried to make him as awkward as possible and just overly excited about everything.

J-14: What was it like flirting with Kristen Stewart?
Justin: Her character is just really awkward. So you put two really awkward people together and it’s just a really funny thing to see them try and have a fluid conversation.”

See the whole Justin interview on J-14. Via Twilight Examiner