For some time, I've thought that modern shoes are just as bad for walking as they are for running. I often see people walking with giant steps that land heel-first, and this looks terribly inefficient and painful to me. I don't think anyone would walk barefoot on a hard surface this way.
The above video shows a more efficient way to walk. Just like with proper running, the key is to land with the feet under the center of gravity. I think of myself as a compact walker. I try to keep my feet underneath me while "walking the line". I feel it's also helpful to cut down on unnecessary upper body movement as well.