Once upon a time I used to put my left foot down when stopping. Then one day I put my left foot down into a puddle of motor oil at a red light and promptly hit the asphalt, much to the enjoyment of nearby motorists. After that day I come in for a landing with both feet down, and once I've come to a complete stop I keep my left foot down and put my right foot on the rear brake. Regards, H.C.D.
I just recently completed the MSF Basic Rider Course, so I now have a different answer. Simultaneously: left hand on clutch, left foot downshift to first, right hand on front brake, right foot on rear brake. Then left foot down. Hope I said that right.