OK, you already know how to walk. Having said that, there is often room for improvement. Here are some examples:
You can increase the energy efficiency by altering your centre of gravity and by optimising the width of your stride.
By looking at the horizon, rather than at your feet (a very common habit), you will be lighter and more forward in your movement. You will have to glance down from time to time to check the footing, but keep your head up and keep your gaze forward as much as possible.
Ensure you are not wasting energy moving side to side or bobbing up and down when you walk. It should feel more like gliding smoothly.
Your arm swing should mirror the rotation taking place lower down as you move. This trunk rotation allows fluid forward movement. As you quicken your pace and take longer strides, you should also find your arm swing becomes more exaggerated. Be sure your arm swing movement is coming from the shoulder, not flicking at the elbow, which is a common inefficiency.
Breathe fully in and out. Silly thing to advise, but many people do not relax and breathe when walking.
Lastly…smile and enjoy. More and more research tells us what many already knew…being outside and being active are good for both your physical and your mental wellbeing.