Subway Doodles Sketch Underway V5

Days ago I started a new journey of creating subway doodles. My art instructor,  recommended I try to develop doodles on the subway. He mentioned that this would be a way to practice my eye accuracy. However, my goal is to practice his technique. In fact, a few days ago, I created a video called How To Draw Proportional Spray Can? Thus, when should I practice his way and is there a way I can still blend into my daily trips?