Whether walking or running, I try to do it in pretty places. The idea is to incorporate some sense of spirituality to it. I swear, this helps more than is rationally possible. I once walked up a fjord in Norway. And I've run around the Acropolis. But cute-neighborhood USA works pretty well too.

BTW, unrelated: I've started taking breathing breaks. Quiet, relaxed, and possible even in a busy place. I do 20 deep breaths, about 15 seconds each. Eyes closed and I try my best to empty my brain. It really helps.