Well the point of doing a tantrum is to get what they want so i think just leave them there to scream and yell all they want till they realize they are not getting what they want and thats it. Cause sometimes the more you pay attention to them the worse it gets.
If its not in public, let it run its course. Stay calm, and he/she will eventually stop when they realize that they arent getting any kind of reaction or special attention. Dont draw attention to the negative behavior, instead encourage them when they have good behavior.