Well starting with 90 degree squat then progressing slwoly. However technique has to be emphasized and strictly adhered to. You must check for any muscle or other imbalances. Injury is common even for young athletes. When I used to play football I used to see many injuries or onset soreness because of the deep squat. So stregthen all the muscle’s in the legs and upper body first. The squat is a total body overall strength exercise just so not forget that.