I mentioned last time marching in place in front of a mirror. I find that simply marching in place tends to automatically put the legs in proper alignment. While there are many runners who do just fine being slightly duck-footed, I think it is optimal for the feet to be pointed forward. Having feet, or one foot, that point out a bit will tend to cause excessive pronation. Pronation is the collapsing inward of the ankle along with flattening of the arch. Some pronation is normal, and probably absorbs shock when we run. Excessive pronation can, over time, cause twisting forces in the leg which can lead to injury.
So, as I said, the marching exercise causes our feet to point straight forward, and puts the knee, ankle and foot in proper alignment. My left foot used to point out more than my right, and this eventually led to an ankle injury. After discovering the simple marching exercise, and then adding the one-legged stance on each leg, my ankle pain suddenly disappeared. Stopping on one leg, letting our weight settle on that leg, and achieving good balance on that one side, then the other, is an important addition to the marching exercise. This simulates our pose at mid-stance, and if we can make this stable during the marching exercise, we will have more success being stable in this stance when we run. Stability and balance at mid-stance helps us avoid injury. The cumulative effect of being slightly off balance for many miles is possible injury. For me, it meant problems with my ankle. For others, it could mean knee, foot, hip or other problems.
It is important that the foot fully settle (with the heel touching the ground) when doing the exercise or when running. There should also be a slight bend to the knee.
I have included a picture of me in the middle of my last marathon. You can see that I look pretty good in mid-stance. My foot is fully in contact with the ground, it is pointing forward, and I am not displaying excessive pronation. There is also a slight bend to the knee.