Catherine Hardwicke has answered a bunch of fan questions. They are posted over at The Twilight Saga website. Here is a sample:
Lynn: When dealing with your actors, were there any special exercises you would have them do to help them get into character?
CH: We sometimes did improvs of scenes that weren't in the film -- like we rehearsed Bella's phone call to her father, asking if she could come live with him. We also had a choreographer come teach a "cat class" -- showing us how predators move when stalking their prey and fighting. Nikki and Rachelle especially got into it -- we almost had a delicious CAT FIGHT.
Marjie: Hi! I just was wondering, what was it like off-camera? was it crazy? who was the prankster in the cast?
CH: Rob was a great sport and always had unique, original comments. Kellan has some great "dirty south" moves, and Nikki fires off frequent zingers like "Guess what guys, I just had a baby on Wikipedia".
Go HERE to read the full Q & A.