"Hitting from the top" a fault seen often with higher handicappers is best described as an aggressive or too quick change of direction in an attempt to hit at the ball. Described as "swinging over the top" this jerky swing characterized by an overactive head and right shoulder leads to a loss of power and accuracy. The player lunges forward with their upper body forcing the club to approach the ball too steeply from outside the normal plane often resulting in sliced and pulled shots.
The transition from the top of the backswing into the downswing establishes the rhythm of the swing as is evident when watching a good player. There is no urgency to hit the ball from the top, but rather a smooth coordinated movement of the club and body which allows the acceleration of the club head to peak at impact. Because the lower body initiates the downswing in one synchronized motion it produces a swinging motion of the arms and club which appears effortless.
I would recommend this drill to improve the tempo of your swing during the transition from backswing to downswing. Using a 6 or 7 iron with the ball teed up slightly and your feet only a few inches apart hit a few shots. Swing the club back smoothly and let your lower body unwind to initiate the downswing. Focus on a fluid transition allowing the club to fall before releasing it through the ball. Keep your head steady as your downswing starts which will allow the club to approach the ball from the inside, on a shallower plane resulting in more solid contact with the ball.
After hitting a few balls you will begin to sense the swinging to the club head through the ball rather than hitting at it. Best of all your swing will feel effortless and your shots will fly straighter.