I often use this exercise as a quick left-hand warmup. It's great for loosening up your left hand, especially for more complicated chordal work. It's also an excellent study for left-hand coordination and control.
The concept is to play chromatic octaves starting on the low open E string entirely in first position. We will move up chromatically starting on the low E up to the G# on the first fret of the third string. We will use open strings as needed.
To execute the exercise properly, we need to make sure the left-hand fingers play the octaves at the same time. The octaves utilizing open strings will be easy, but the octave fingerings that utilize two fretted notes will be more of a challenge.
When playing an octave that uses two fretted notes, we want to make sure both left-hand fingers land at the same time. Remember we are in the first position, and your first finger will play all notes on the first fret, your second finger covers all notes on the third, and so on. There are no position shifts.
You can play the octaves in unison or as jumps. In the video lesson below, I play them as jumps using hybrid picking. Hybrid picking is not required for the exercise, but it allows me to play the exercise at top speed, thus presenting the greatest challenge for my left
Lastly, remember to keep your left-hand fingers curved and to play on the tips of your fingers. Start slowly and work it up to a finger-twisting frenzy!