This sketch started in Harmony with the box brush, (the Harmony project at mrdoobs.com/harmony which I've mentioned previously now has an Android app.) After filling the page with the box brush I brought this background SketchBook Pro and created a layer and imported drawing or background. At that point I started filling the background with sketches of faces until I found one that I liked. I would use the box shapes and masses where I could to guide the placement of faces, but ultimately the face that you see you there now is the one that I chose out of about six attempts.
After finishing the simple sketch of the face I export the drawing and layered it with subdued filters and then tweaked colors and added some texture. After adding light washes of color I exported again and then added some geometric shapes with another program.
I saved and exported a cropped version.