I need tips on how to help my mourning friend.?

My best friend just had 3 of her friends die in a car accident, the fourth in a coma. I am going to be with her next weekend to help her, and I'm scared of saying the wrong thing. Any tips on how to make her feel better? I'm always afraid of making it worse or making me look like a jerk. I am also saddened by these deaths though I didn't know these people.