I love sketching people when they're moving and talking, rather than posing. I sketched this admissions officer at a meeting for prospective college students. The challenge was to choose a characteristic angle and pose as he spoke.
I'll be lecturing and demoing about sketching people in the wild at the Portrait Society of America's National Conference in Washington, DC this weekend. I don't know if you can still register to attend, but if you can make it, I recommend it highly. Here's the registration form.
During my talk Friday morning called "Likeness and Character," I'll be previewing a segment from an upcoming video that I'm working on called "Portraits in the Wild."