The good news Ben gives to Sal after he reads her palm is that she has let him hold her hand "for almost five minutes and...didn't flinch once".
When Sal meets Ben, she finds him to be much more demonstrative than she is. Suffering feelings of guilt and inadequacy since her mother left her and her father, Sal has a tendency to shy away from love and human contact. When Ben first comes into her life, Sal actually flinches whenever they make physical contact of any kind. Ben notices this and points it out; Sal had not been aware that she is doing that, but realizes that he is right.
One day, Ben offers to read Sal's palm. He takes her hand and stares at it "for the longest time". Finally, when he is done, Ben asks Sal if she wants him to give him to good news or the bad news first. Sal chooses the bad news, and Ben says,
"The bad news is that I can't really read palms...the good news is that you let me hold your hand for almost five minutes and you didn't flinch once".
Sal immediately draws her hand away, and doesn't speak to Ben the whole way home. She doesn't know what to make of him, especially since, when they part ways that day, he leans forward, and, although she is not sure he means to, she thinks he kisses her ear before he walks away (Chapter 20).