Don't start your squat by shooting your butt backwards. Your butt should start to move down first, and gradually move back as you get lower.
Deadlift, your starting position is workable. Stop raising your hips before you pull. Break the bar off the floor from your setup position without changing your back angle. Your hamstrings work here isometrically to keep your back angle from changing. Use your quads to lift the bar from the floor to about halfway up.