Character Clues
Character Analysis
Actions
In The Usual Rules, you can tell how good people are by how they treat others—especially strangers. For example, Wendy can tell right off the bat that Alan is a good person because he lets her loiter around his bookstore and is particularly patient with his son Tim, who lives in a group home for autistic individuals. And even though Wendy often worries that she's an awful person because of the fights she had with her mother, we know she means well; after all, she befriends Violet and offers to help her care for Walter Charles even though she barely knows the girl.
Family Life
You can get a read on characters' personalities by how they treat their families. Garrett's treatment of Wendy—including largely being absent in her childhood but now attempting to make amends—shows that he was really irresponsible and reckless but is now more mature and realizes the error of his ways. Now, he wants to be a better father.
Garrett's mother, on the other hand, never even seems to consider accepting her son for who he is or showing him any kindness. And it's clear that Josh is a loving and kind person because he does everything he can to make Wendy feel like he loves and cares for her like a "real" daughter; in fact, he considers himself her parent, even after Janet dies.