I teach drawing from observation. I start off with talking about projection and drawing machines then show them how to create their own 'conceptual'mdrawing machine using nothing but the straight edge of a pencil. The trick is to identify points in the scene (intersections, corners, features etc) which corespond to each other on a vertical or horizontal axis. with a few of those done, the whole drawing drops into place.
Edit. Unless I am missing something, I see no mention of Van Goghs sighting grid. Crude, but effective.
As you imply, drawing from observation is a skill that is best taught in person. The students mostly learn from being corrected, which I do directly to their drawings.
However, I did put together some material on the subject. I'm not sure how useful it is (some of it could have been better written).
My approach is not significantly different to that which most competent drawing teachers would employ. However, I believe that my use of language is a bit more consistent and exact than most artists, who tend to be a bit hand-wavey in their language usage. Practices that are termed one thing in 'book a' are termed something completely different in 'book b'. I learned the value of consistency and exactitude from collaborating with computer engineers, which is one reason I like lurking in HN.
Edit. Unless I am missing something, I see no mention of Van Goghs sighting grid. Crude, but effective.
http://www.vangoghreproductions.com/art-techniques/perspecti...