Solid drawing is the animation principle which makes the drawing looks Three dimensional and believable with Volume, Weight and Balance.
This requires the knowledge of drawing a subject three dimensionally.
With Solid drawing you will able able to draw figure 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 isometric flat cube.
Here is the rough pass of designing the character with the solid shapes.