The only way that your movements will be fluid is if you DRILL! So here are a few drills for you to work on. How you practice is how you perform... how you practice is how you form your body. So practice with good posture!

Tuck under your pelvis

Hold firm in your Abs

Soft in your knees

and NEVER do anything to the point of pain! here is not a no pain no gain form of exercise! If it hurts stop and consult a teacher or physician!