In the summer of 2018, I had the pleasure of being taught by an ex-Disney 2D animation supervisor to analyze action and anatomy, and apply it into figure drawing. Here is what I learned:
Level 1: Develop hand-eye coordination & muscle memory > Focus on form-drawing
Level 2: Improve your fundamentals of sight-measuring and chiaroscuro
Level 3: Make a thousand mistakes to create a single great drawing
Do quick "hovers" over your drawing before drawing it down
In your sketchbook, draw rows /boxes with heights of 2/4/6/8 inches, and draw within those constraints
Shift your sketchbook for difficult angles
Do interval practice using an mobile or desktop app. Each interval can be 30/60/150/270 seconds long. The longer the interval, the more details you have to draw.
Your sketches does not have to be perfect. The key is to fail quickly, develop muscle memory, improve hand-eye coordination
Analyse your subject and use the right references
For learning anatomy, focus on drawing one part first eg. hand, then legs, torso, etc.
Constantly look at your subject and your sketchbook back and forth when drawing
In 60 days, fill up four large sketchbook (11"x14",100 sheets each), front and backside of the sheets which equates to 800 pages in total. Hence, you would have to draw about 13 pages every single day.
Practice, practice, practice. Then practice, practice, practice. 4 hours each day is the minimum. 6 hours is great, all day is the best. - ex-Disney 2D Effects supervisor