Watch the Harmony Lead: 5 online guitar lesson by Robbie Calvo from SoloCraft
I'm going to play the D major scale for you in this example starting on D and you are going to be my second guitarist in the band and as I play, you are going to play the D major scale starting on F# all the way up to the octave of F# and back down again giving us a 3rd harmony above my melody. Got it? Good! That's how you can figure out your harmony parts a third above a melody.