Have you spent any time making a conscious effort to have your feet straightish?
Being more aware of your positioning and changing it when it is incorrect is a good place to start.
Do you have restriction in your ankle, feet, or hip?
Hip internal rotation is one place to start.
Here are some others to take a look at.
Episode 343: Stop Walking Like the Duck You Aren’t
Squat Quick Test: Is it Tight Ankles or Tight Hips? | Community Video
Pro Episode # 38 – MWod Pro-User Request Friday: Femurs Straight, But Feet Ducked? The MWOD Approach