comforting someone through grief

This news came out of the blue. One of my close friends from high school recently lost her mother to breast cancer. And I feel like it's important to come back home and offer whatever support that I can. It's a sticky situation because I'm not good in situations like this... How do you know what to say to someone after they have lost a parent? What will bring comfort? What if you say the wrong thing? Well, I pray that I figure it out.