Watch the My Chick - Middle Strings online guitar lesson by Matthieu Brandt from Guitar Lab: Triads and Hendrixian Double Stops
We'll look at the third position to play the three triads for the I, IV and V chords in. The shapes will be the exact same ones we encountered in the previous lesson, but their function in the key will be different.
Keep your eye on the root of the triads to establish the shape. Although we're working in one key only (the key of G) this principle and the relationships of the triads is the same in every key. Locate the tonic of the key first, then locate the I chord triad and then it's IV and V triad shapes in close proximity.