I have been doing a drill where I swing with my right arm only (right-handed golfer). In taking the club back slowly with my right arm only to the top and pausing there, I have found that the only real efficient way to initiate the downswing is for the lower body/hips to rotate towards the target. The lower body is needed to tug/pull the upper body/right arm. The momentum created on the downswing of the right arm does not have the left arm to get in the way and stall the swing. I find that the body opens up fully to the target without thought or concentrated effort involved.
So practice a full, slow backswing with a pause at the top with the right arm only. Then do a good downswing and the body will be facing the target and there is also some good lag and forward shaft lean.