Watch the I ii iii IV vi IV vi V Etude Level 1 online guitar lesson by Vicki Genfan from Open Tuning Handbook: Rhythm

We're using the diatonic chords, moving up in what's called an ascending bass line. Then we vary it by going to the vi chord. So much of what makes a song interesting has to do with just this – giving the listener a repetitive progression, melody or rhythmic pattern, and then changing it up so they don't get lulled into oblivion.