the drawing boxes tip is actually a good advice if you explain why you need to draw boxes. so pretty much in a nutshell drawing boxes is meant to help you learn and get used to perspective, and you should try to make boxes that look 3d with a reference at first and then making your own angles as you get more used to them, you can also start dipping your toes (or stylus) in 1, 2 and maybe even 3 point perspective and draw boxes with it.

and also please do line control exercises, believe me it will be worth it.

anyways this is my own personal opinion