Pillow shading is shading by surrounding a central area with increasingly darker bands. Pillow-shading is bad because it pays no attention to the light source, and conforms to the shape of the area rather than the form it represents of how light affects it. Pillow shading is often, but not always, combined with banding. The way to fix pillow-shading is simply to pay attention to the direction light is coming from:
The reason pillow-shading is wrong is not because the light source is frontal (from the viewer's direction). You don't have to place the light source in the corner. The reason pillow-shading is incorrect is because it follows flat shapes rather than focuses on how the three-dimensional forms are lit.
So, it is possible to use a frontal light source, so long as you pay attention to the forms: