Drawing Perspective

I accidentally skipped a chapter today and leapt to the one about Perspectives. I learned about the concept of Vanishing Points and Converging Lines. Here's our library (minus many details like the view outside the window, the blinds, and the carpet.) Those cabinets frustrated me the most, and there is an obvious lack of shadow grading. Why can't I see the different levels of darkness clearly? 

My one-point perspective

Our library with a sofa, a TV on the left, and a reclining office chair 

I was wondering why I found it hard to start this, considering they were mostly vertical lines; but when I went back to the chapter I had missed, I understood -- it was the lesson on Basic Unit. Now I've read it, and I started to do the exercise on drawing negative spaces, but my brain and eyes must be tired, because I wasn't progressing well. It also involved my ultimate waterloo: proportions. This was the first exercise that required me to scale up the drawing, and as expected, I was struggling. I'll continue the drawing tomorrow. 

P.S. Drawing is not easy.