I found that the biggest obstacle to a fast left hand is more mental than physical. We spend time training our hands to be fast but we do not train our minds to be faster. This is something you can practice away from the bass. I literally like to practice difficult left hand hand passages by "playing" them with just the left hand and imagining my hand on the fingerboard. I know that "air bass" sounds silly but the biggest part of playing fast is knowing what your left hand is supposed to be doing. "Play" through the line in your head making sure that you clearly imagine yourself playing every note in the passage. This trains you to be accountable for every note and allows you to hone in on the left hand without all of the other distractions of playing bass (like guitarist and drummers
). The great part of practicing this way is that you can do it most anywhere at any time and you dont take up your actual bass time.
