More people, including one of myself(below-left)....
Yes, more tips
16. When there's no one to sketch and it is dark outside, the windows in the train and bus serve as "good mirrors"-giving us a reflection of ourselves. Good time to do a self portrait.
17. Whatever medium you use to sketch, always have a small one for detail and lines and a big one for tones and shades. When I use pen and ink, my small one -is a black ball point bic biro and my big one is a Tom Bow Wash Brush Marker Number 75. When I use graphite, my small one is a 0.5 or 0.7 mechanical pencil and my big one is a chunky broad round shaped graphite stick. It helps to use both simultaneously. Sometimes you can decide to start with the big and finish up with the small or start with the small and block in with the big.
18. If someone is beside you and not in front of you and you still can’t resist sketching them. I would advise, you look for a while and then sketch from memory. This keeps you from turning your head to the side every so often.
19. I sketch by watching the movement of the angles in which the head is positioned. Angles are great for learning the way to sketch. If you get the right tilt you’ll be very close to getting what you want from what you can see.
20. To get the best people to sketch, don't sit in the direction the train or bus is moving, most commuters sit that way and if you sit that way too you'll not get many faces.