I haven't read Drawing on the Right Side of the Brain and while I'm sure it's a helpful book the Stravinsky exercise and grid drawing seem like inane shit to me.
If you want to learn to draw there must be something you want to draw, so draw that not Igor Stravinsky. Draw whatever you want and be critical of it, not "The leg is a little off" critical but "How could I do the whole thing better?" critical. Identify what you need to improve and study it.
Immerse yourself in good art and other interests. Building taste is what fuels your desire to improve.