John Prine is an American treasure as a songwriter and entertainer. His debut album in 1971 introduced the world to a handful of poignant classics. John's fingerpicking is very basic but melodic and effective.
Illegal Smile is typical for his style, with a catchy hammer-on in the bass followed by what I call generic picking, meaning it never has to be the same but there are some simple parameters, which are described in the lesson.
The song changes into a 3/4 strumming pattern in the chorus, then kicks back to the intro before each next verse. The transitions are also very basic.