Excerpt:
The hardest part of playing multiple notes with the right hand is training your pinky to come down in the same spot every time. Because it's the most difficult finger to get cooperation from, most guitar players tend to ignore it or avoid using it altogether. This exercise will help to strengthen your pinky and get you ready for some of the more complex stuff to come.

Tap with your right hand first finger on the 17th fret, then tap with your right hand pinky on the 21st. Use your right pinky to pull back off to the 17th, then pull, pull, hammer and repeat. Then drop down to the B string and do the same thing. Move down a couple of frets and repeat it.

You can play this over the chords A E G D then if you want to continue, drop the whole thing down a couple more frets and use it over the chords G F, C then end on B.