To work on your cast, check out this playlist
Steve Stricker, this years Presidents Cup captain demonstrates textbook sequencing and textbook upper body control. If you maintain your chest position with good sequencing, you’re swing will look smooth too.
Another key to Steve Strickers smooth swing is having very little wrist movement in transition. His transition comes mostly from the body. If you struggle with a cast, then you need to learn to move your arms with your body instead of moving the club with your arms.