Form Errors
Below is the result of a study of 62 published running form error documents that noted 270 errors.
The 'Media' column are documents written by authors who generally do not have an in depth personal knowledge of running form. The 'Health' column are documents written by people who study and/or work with runners on a daily basis (Physical Therapists, etc.).
The three yellow rows are basically the same issue in that they generally all occur at the same time. The two purple rows are largely the same issue also in that when one hip drops, then knees tend to collapse inwards.
The media tended to have higher counts/mentions on the more visible things like being tense and arms swinging across the body.
Conclusion:
Concentrate on ensuring you are not making the most common run form mistakes:
Overstriding, slow cadence, and heel striking
Unrelaxed upper body
Hips not kept level side-to-side thus knees collapsing inwards
Swinging arms across the body
Poor Posture