The shoe should be light and flexible. It should keep your foot in place and feel comfortable. There should be a space between your toe and the toe of the shoe. If you can't find a whole block of time, it's best to walk for 10 minutes four times a day. You are more apt to keep it up.
Good posture is important.
Walk with your chest up and shoulders back. Your chin should be parallel to the ground, looking straight ahead. Tuck your buttocks under your hips, pulling in your abdominal wall muscles. Your feet should be in line with your body, with the toes pointing straight ahead. Your arms should be bent at 90-degree angles, holding your elbows close to your side and swinging them between the breast bone and the hips.