Nothing gets you more in the spirit of drawing than some intense Preston Blair drawings. I haven’t finished those, but I had done enough to get me really focused on a nice sketch of this Bengal kitten, called Kimburu Filfil Falconer.
The sketch wasn’t really constructed, just drawn from reference, as-is. Of course, I had to measure some of the parts, like the overall length of the body, compared to the size of the head. With the Preston Blair drawings still fresh in my mind, including the requirement to see proportions (without that, you cannot make those drawings), it was actually not that difficult.
It seems if you want to improve your art, the best thing you can do is to give yourself a really tough challenge, that requires your complete concentration (no music!), and then return to what you thought was so hard to draw. It suddenly is much easier.
That is all.