Watch the I vi ii V Etude Level 2 online guitar lesson by Vicki Genfan from Open Tuning Handbook: Rhythm
The "Travis picking" pattern combines bass notes with syncopated notes on the higher strings. Often times the bass notes are alternating, especially if the root of the chords is on the 6th or 5th strings. This etude adds the hammer-on technique to the basic Travis style picking pattern. If the pattern is new to you, take your time and get it in your hands and fingers before adding the hammer-ons.