True, I currently have a student I am tutoring who wants to learn "how to draw properly". So I have been thinking through some drawing exercises and principles with him. It's all about looking, isn't it? Really seeing those lines and angles, understanding and interpreting the changes in direction in a curved line, and obeying what is directly in front of you as if it is a flat series of points and distances as you map it all out. If you can really see and get a line or gap or curve, drawing it is a doddle, especially if you develop a sketchy style - it will always look true in you understand and deconstruct what you see, and if you are rigorous in critiquing your own work.
I have spent years and years drawing separately to looking live. I have concentrated on and loved more abstract drawing, and if I have made sketchy drawing of real things, I have preferred to work them out in my head first.
So I have done these exercises in drawing, and I still very much look at things with such accuracy when I am making work, but it's along time since I sat down and tried to represent a table and two chairs in front of me. Why would I? And yet yesterday I felt very moved to do so. It was a little problematic with not having my preferred choice of pens/pencils, etc, but no excuses. they're not too terrible - there are some accuracies - they look believable even though you don't have the objects in front of you to compare. I haven't really got my eye back in yet, but again I surprise myself by feeling that I will continue this. More to the point - I can understand where I go wrong, what I can't see.
I do that thing of changing scale throughout the drawing. Also, I know there are some things I just can't see - i just couldn't work out the table-top shape - it's got a wobbly wavy edge as well as that oval-top shape which often turns out a bit wrong. Once you can trace with your eyes along the line or shape or outline of each side or edge, the hand draws it easily. the eye stops interpreting objects as things and sees them as angles, distances, lines directions, in relationship to each other.
You can see they are tentative drawings.