Miss Maudie presents Scout with lots of good advice during the course of the novel, but perhaps her most important contribution comes when she explains Atticus's previous warning about it being " 'a sin to kill a mockingbird.' " Scout is uncertain of the real meaning of Atticus's message until Maudie explains that the mockingbird is an innocent songbird
"... that don't do one thing but make music for us to enjoy. They don't eat up people's gardens, don't nest in corncribs, they don't do one thing but sing their hearts out for us. That's why it's a sin to kill a mockingbird." (Chapter 10)
Maudie's explanation helps Scout to understand that mockingbirds come in human forms (Boo Radley, Tom Robinson) as well.
Scout also offers up an abundance of advice, but it mostly comes from a future perspective that seemingly gives her a wisdom far beyond her years. During Uncle Jack's Christmas visit to Maycomb, Scout learns a great deal about the Finch brothers and the upcoming trial of Tom Robinson by eavesdropping late at night. When Atticus suddenly announces that Scout--who believes she is secretly hidden from sight--return to bed, she is mystified by the scope of his vision.
... I never figured out how Atticus knew I was listening, and it was not until many years later that I realized he wanted me to hear every word he was saying. (Chapter 10)
Read the book!