i would say elbow and shoulder would be most common.
squat and deadlifts really aren't the most popular lifts to be done. bench, curls and tricep pushdowns are the most frequently done exercises causing stress at the ligaments of the elbow and shoulder just from overuse. those i think would be the most common. easiest way to injure yourself i would think would be with poor squat form and weak abdominals causing low back pain.