If you already have a decent backswing, the downswing should be a very natural feeling.
The "correct" sequence is:
1. Shift weight from right foot to left foot
2. Start rotating your hips
3. Let the club start coming down
4. Weight is now 70% left 30% right
5. Unwind shoulders
6. Bring arms down
7. Uncock wrists
8. At impact, your hips should be open, your shoulders should be slightly closed, your torso and head should be behind the ball with driver, directly over it with irons. Your wrists should be uncocked and rotating but not "flipped."
9. You should end up with 90% of your weight on your left foot. Your belt buckle facing the target, your hands high, and your right heel off the ground.
Reading this, do you think you could perform all the actions correctly, in the correct sequence, in the <1 second it takes for the club to swing down?
Actually, yes you can. But not if you're consiously controlling it. Your body knows when to tighten or relax different muscles. The biggest error in timing the downswing is either rushing with the shoulders and wrists, or thinking that you somehow have to help your body swing the club.
Think of it this way. When you were a baby, you learned to talk by babling incoherently. Your body remebered what toungue positions produced what sound. Eventually, you could produce those sounds at will, effortlessly.
Now, can you imagine what would happen if babies learned to talk by studying the nessecary toungue positions? What if babies learned to speak fluently before they learned to walk. No doubt, we would be coaching them on when to shift their weight, how to swing their arms, etc.
Why, then, do we try to consiously control our golf swings? We all have the potential to hit great shots; We know, because we've all done it. But it probably happened when you weren't thinking about anything. If you hear athletes talking about being in the zone, or playing out of their minds, that's what they mean; They are playing up to their potential by not interfering with themselves.