There’s no one universally desirable running form, any more than you would expect all baseball players to have the same swing. We each run the way we do because of the unique way our bodies are put together—the length of our torso in relation to our legs, the shape of our feet, the alignment of our bones, the communication between our brain and central nervous system, and a million other things.
So you run the way you do for some inherent reasons, and to a certain extent, you shouldn’t try to change that. At the same time, we all have a range of how well our unique form manifests itself. When you have weakness or tightness in one or more places in your body, your unique form will move toward the less desirable end of its range. Probably when you were a kid, especially if you had an active childhood, your form was toward the more desirable end of its range.
By building a stronger, more supple running body, you can ensure that you’ll usually be moving with the more desirable version of your running form. That’s going to include your personal version of these elements of good form: landing over your center of gravity; a light, rapid cadence; minimal lateral rotation; and easier to spot than quantify, relaxed body position.