The best way is to watch and learn from someone who does it, like Sam at exquisite creations, he`ll probably be at Olympia.
I drill from underneath the nail, supporting where you`re drilling into, take it slow and you can feel when you`re through the nail as you reach your finger. Then reverse the drill to come back out of the nail. You do need to make sure you have enough length on the nail for placing the nut is you use a post with your charm. I hope I have explained that properly but it is so much easier to watch someone than to describe it