So I am starting 5×5 Stronglifts and I am trying to construct a mobility routine, what would be the best way to go about preventing injury/become more flexibile to do more squats ?
Depends what is going on with your squat.
Preventing injury having proper squat technique is step one.
Are you prepared for the increased volume with squatting?
Have you done a search or gone through episodes for episodes which address different aspects of squatting?