Can you practice that? Do I learn anything? I don't know. I might be flexing the same old muscles with 2 pound weights when it comes to improving my drawing. It passes time, though.
I've noticed improvement in my work when I've spent time drawing from life, from photos, or doing studies of other aritsts' work. I used to believe that making up heads was good for me; encouraging me to invent things and call upon the skills and the knowledge that I've gathered from my studies. I don't know. Maybe I'm just wallowing in the shallow pool of observations I've made in the past.
Anyway. Here are more improvisational heads-- are they worthless? Or maybe they're worth a click and a comment. You decide!
Drawn on real paper with pencils and pens, scanned, and vandalized (colored) in Photoshop!