Have you tried dry fire? This helps a bunch. Do this for 20 minutes every day for 2 weeks and see what happens. Take a black tack and stand 15 feet away. The black tack will give you a sight picture that is about right for a 200 yard target. I also bury my elbow in my support side. A hard back helps too.
Hold your rifle like you mean it. Check your NPA. If you get too relaxed during dry fire the rifle will kick, not so much with a AR but a 30 can hurt. Practice calling your shots when dry firing. Do not have any ammo close by when dry firing.
I have found I shoot offhand better if I keep my elbow up for a wood gun and elbow down for a AR. Your milage my vary. Good luck.
God Bless our Troops especially our Snipers.