The second transition in the golf swing (the first being the takeaway in which we transition from a static to a dynamic state), is not the start of hitting the ball, and golfers who think it is ruin everything they have done right up to that point. We are still preparing for the hit, even when we are coming down into the ball. We do this by making the start of the downswing a gravity move.
By that, I mean the club drops down without any direct effort applied to it, being only carried by the body turn. Do not ring the bell (pull down with the last three fingers of the left hand). Certainly, do not push the club down with the right hand. Remember what we said in a previous post about pushing things.
By letting the club go along for the ride, we let it begin accelerating naturally, so when the moment comes to swing the club into the ball, it will already be ripping through the air. To push the club downward at the start actually slows the club down.
A good way to coach yourself to let the club fall on its own is to monitor the feeling you have on the inside of your hands, the part touching the club. When the club reaches the top of the backswing and is suspended momentarily, the grip feeling should be quite light, and should not change when you start down. The right thing to do is to carry that light feeling into the downswing–well into it. That way, the club cannot be forced into the ball.
Another drill you can do, even more extreme, but certainly not wrong, is to swing to the top of your backswing, and, as you start down, relax your grip and let the club fall out of your hands as you continue your swing motion with your body and arms. You can get no more effortless than that. Try this a few times, then swing one more time and keep hold of the club, but swing through the ball with the same light feeling as you had when you let go of the club.
I believe you will shortly find your clubhead speed increasing, and it might even be scary fast. Because you are not forcing anything, you will not lose accuracy, and might instead gain some.