What I do is try to play the same riff or melody that I play in the lower or middle octaves in the upper octave.
A good song to do this on is "Heartbreak Hotel" with the opening lyrics:
Well since my baby left me I found a new place to dwell It's down at the end of lonely street, at Heartbreak Hotel
On the middle octave, the tab (that I play) is: 6B 6B 6B 5D 4D 5D 6B 6B 6B 6B 5D 4D 5D 6B 6B 6D 7D 6D 6B 5D 4D 5B 5D 5B 4D 3D 4D
On the lower octave, the tab (that I play) is: 2D 2D 2D 2D'' 1D 2D'' 2D 2D 2D 2D 2D" 2D 2D" 2D 2D 3D" 3D 3D" 2D 2B 1D 2B 2D" 2B 1D 1B 1D
So on the upper octave, the tab (that I play) is: 9B 9B 9B 9D 8D 9D 9B 9B 9B 9B 9D 8D 9D 9B 9B 10D 10B 10D 9B 9D 8D 8B 9D 8B 8D 7D 8D
Playing just the "Well since my baby left me", alternating each octave is a great exercise.
Add the little riff: 10B 10B 10B" 9B 9D 8D 9D 9B to the end, and do the similar riff on the other octaves... have fun with it !
Ken H in OH