This is just a simple honky-tonk riff... there are 3 variations depending on the chord throughout the song.  

Variation of Em riff:  
G---------------------------  
D---------------------------  
A---------0--2-2--4-2-------  
E-0-0-3---------------------  

Variation from Am riff:  
G---------------------------  
D---------0--2-2--4-2-------  
A-0-0-3---------------------  
E---------------------------  

Variation from Bm riff:  
G---------------------------  
D-----00---44--66-----------  
A-22------------------------  
E---------------------------  

The verse is as such:  Em (x4), Am (x2), Em (x2), Bm (x4), Em (x2)  

Chorus: Am (x2), Em (x2), Am (x2), Em (x2), Bm (x2), Em (x2)