Solid drawing is the animation principle which makes the drawing look Three dimensional and believable with Volume, Weight and Balance.
This requires the knowledge of drawing a subject three dimensionally.
With Solid drawing you will be able to draw figures from any side, which will help in animating your drawing.
When drawing the cube, Avoid making parallel lines. The lines should be bend towards the vanishing point otherwise it becomes an isometric flat cube.
Here is the rough pass of designing the character with the solid shapes.