Initially I followed the instructions and drew through the doorway by hand without using a ruler. Having done that I checked by eye level. Then I drew the green lines to see how accurate I had been with the initial drawing. Not very accurate! The angles are more acute than I had thought. I then drew the red lines to see where they should have been.
This was a very quick sketch but i showed me how easy it is to start off on the wrong alignment. For some reason I find the concept of perspective really difficult. When I have to think about it I get it the wrong way round but I have checked some of my previous drawings and some are accurate.
I think it would be good to put down my initial lines so that there is some spontaneity and then check them for perspective before moving on.