Watch the Surfer's Mambo online guitar lesson by Jason Loughlin from Essentials: Surf Guitar
The first melody starts on the root and descends chromatically to the b9 of the V chord. We resolve it by sliding into the D7 shape at the tenth fret. Then, we walk octaves down chromatically from the root to the 5th. While still on the V chord, we're gonna move from one triad to another chromatically. I start with a 5th, b7, and 3rd inversion, and move it up chromatically to the b7, b9, and 5th, and back down again, resolving on a Gm triad. I use this a couple more times in this etude, but they're all used as a device for connecting chord tones.
The major sounding section of the tune centers around the F major chord. This is played with double stops as way to help distinguish it from the minor section. The melodic motif is a suspension. Beat 1 of each measure starts with a double stop a step above and then resolves down to the chord tones.
In the last section of this study, we have a quicker harmonic rhythm between Gm and D7. Now they get just two beats each. This gives us an opportunity to use triad inversions to ascend and descend through the changes to help hide the fact that we're just going back and forth between two chords.