This is the trick and tips on how to start downswing.
The Right Start (Left Picture)
When you move from bottom to top, move your weight to your front foot. The little forward bump will cause the hands and arms to drop inside, which will give you a strong move through the ball. Rotating body as hard as you want is permitted. You must make sure that your weight goes toward the target before you start.
The Wrong Start (Right Picture)
It’s wrong if you just turn from the top. Many golfers think that it is enough to turn more so they will whip their hips around when starting the downswing. This is not good because the arms and club will be thrown away from the body due to the open left side spins.
Source: www.golfdigest.com