The same way with open chords or when fretting individual notes. Directly behind the fretboard, but not on or hovering over the upper edge (Low E). Instructors Lisa McCormick and Anders Mouridsen both have full tutorials on this. Also, instructor Christopher Schlegal has a great beginners tutorial called the axis of power, which explains proper thumb positioning.
Am I the only one who plays multiple instruments? Let's be inspirational and find our muses everyday!
