Imagine you have just confronted an armed criminal and you have the drop on him. Now you want to disarm him and take control of him until law enforcement arrives. Some will use the command, "Put your hands up!" Others may say "Drop the weapon!" while others will order, "Show me your hands!" In fact, none of these commands may be the best method of dealing with the criminal.
If you think about it, in each case you are ordering the subject to move. Once he starts to move, you now have to decide if he is moving in order to comply with your command or moving in order to press his attack. It is a reaction-time issue. If you hesitate in trying to determine what the attacker is actually doing, he may be able to beat the drop on you. That is, he may well be able to get a shot off before you can evaluate his actions and make the proper response.
I would suggest that "Don't move!" is the best order to give to the attacker. I often followed it up with the admonishment, "If you move I will shoot you!"
Once you determine the criminal is willing to comply with your order, you may follow it up with other commands. I never liked the idea of telling someone to drop a firearm—too many bad things can happen. I would rather tell him to bend over slowly, very slowly, and put the gun on the ground. All of this is best done once you have taken advantage of protective cover. Then, it is a good idea to command the criminal to put his hands on his head, turn away from you and lie face-down, spread-eagle on the ground. If you can get the attacker in this position, he is not going to be able to move very fast should he decide to attack.
Finally, when dealing with a criminal who won't follow commands, or when dealing with more than one attacker, it is far better to create distance and use protective cover. In the end, your goal as an armed citizen is to stop the attack, not apprehend the criminal. We hold them for law enforcement only when they are willing to comply. Giving some thought to your commands and using commands that will accomplish your goal is important and will undoubtedly be critical to your own safety.