Watch the A Rag online guitar lesson by David Blacker from Lone Wolf Blues
Here in "A Rag" we explore a folk/blues ragtime style piece. It moves at a pretty quick tempo so take it slow at first.
As in Dusty Roads the melody really revolves around the root and the dominant 7th. Getting this sound in your ears will help you create your own melodies in this style.
For this playing style I really recommend listening to the playing of Blind Blake. The album entitled The Best of Blind Blake is a great place to start. Check out the tune Wabash Rag for a similar style fingerpicking approach.