What the best way to deal with a tantrum?

Timeouts work well for me.  I have a "special" rug.  The time out rug!

I was lucky. My kids never really threw tantrums. The few times one or the other of them got overly whiny and thought about throwing a fit, I always joined in. It's amazing how quickly the whining and jumping about will stop once they see (and hear) you doing the same thing!

Meanwhile, you might consider trying this: If the tantrum is thrown at home, walk away from it and ignore it completely. If it's thrown while you're out, immediately leave wherever you are and go home. Upon arrival at home, the child goes directly to his or her room (where there should be nothing to do except sleep or stare at the wall) and stays there until whatever time period you specify.

Enforced boredom cures a lot of negative behavior.

Stay calm. In a firm voice tell the child they "need" to stop. You can not understand what he/she is saying when they are crying.

   If this is not effective, walk away telling the child " I will wait until you are feeling better and we can talk about this.

   Patiently sit near by and totally ignore the behavior. No other comments are needed.Just wait it out.

  When the child regains control simply asks if they are ready to talk.

  Unless the tantrum escalates and the child puts him/her self in danger or others.

Hold the child or remove from area and state "I will not let you hurt _______.

  If you give in, this will re-enforce this behavior and  provide fuel for the next time.

Ignore it. I saw a clip on America's funniest home videos where the mother ignored it and walked away and the child actually moved each time the mother moved. It is for attention as proved by this video. No attention no tantrums.