Try to point toes straight ahead when walking. Put most of your weight on your heels. Hold your chest forward and elevate the front of the pelvis as if walking up an incline.
Stand as if you were trying to touch the ceiling with the top of your head, eyes straight ahead. All the elements of good posture will flow from these simple maneuvers. Good posture not only feels better, but reduces the workload on your back.
Shift your weight occasionally, putting one foot in front of the other and bending the knees a bit to take pressure off the back and put it on the legs. Flex hips and knees by occasionally placing a foot on a stool, bench, or other secure object. When possible, lean against a secure object for support.
Avoid wearing high heels.