Watch the F# Slow Train online guitar lesson by BJ Baartmans from Space Age Rock 'n' Roll Guidebook
The main riff of this song is a typical 2 step "train" groove played to a half-time beat. It's based on the traditional Travis picking style, like Scotty Moore and James Burton would use on Elvis Presley records. However, the new beat gives it a whole different sound.
I'm also using a simple Ernie Ball phaser pedal here that sort of lives its own life as a tone tweaker. It makes the riff pop out stronger and gives the whole song a bit of a spacier sound. The other typical thing in this track is that it's in the key of F#. This give it a cool open string dominant 7 flavor.