Watch the Octaves online guitar lesson by Robbie Calvo from Double Stop Chops
Octaves follow the harmonized major scale exactly as expected: Root plus and octave above will just follow the notes of the scale and the chords found on those degrees. I use octaves a lot in my solos because they are so distinct. Sometimes I'll use one just as a pedal tone idea to add momentum and groove on an outro or intro to a song. Let's take a listen to the octave double-stops against this A Dorian progression.