Practice the basic 3D cube with shading.
Draw another flat form, the pyramid.
Draw a cylinder with shading.
Drawing a sphere is harder than this guy makes it look!
This is a longer video on drawing a sphere.
Practice them all with one video.
Two Point Perspective City Drawing
Trick Art on Paper, Drawing 3D Hole
Draw an Anomorphic Hole Illusion
Floating Ball Illusion