In this lesson you will use the following shapes to play octaves. Keep in mind that because of the way the guitar is tuned, the shape changes (expands) whenever the interval involves a combination of the second and third strings.
The following notation shows how the octaves can be played in the key of C. The placement of the notes is based on Scale Pattern #1, but will sometimes leave the seventh position by necessity:
The best way to succeed in octave playing (and in the playing of all double stops), is to focus on either the higher note or the lower one throughout the line and, using the shape you have learned, let the other notes follow.
As in your previous double stop studies, it will be important to immediately put these shapes to use in melodies.