Unclip as you first apply the brake, put that foot down as you come to a stop. Rotate your clipped-in foot around to where you can push down to get momentum immediately. When you start again, push off lightly with the foot on the ground as you start to pedal with the other. This is, BTW, easier to do while standing, rather than on the saddle.

Just a little practice will make it almost 2nd nature.