The way you say something to a child can make a big difference to how they react to you, especially when they are on the verge of a tantrum!
Choices and consequences is a great way to diffuse a situation, and allows children to understand that their actions have consequences.
Here is an example for you.....
Your little one is throwing toys, and being disruptive.
Get down to their level and look them in the eye.
Say to them "Jack, you can either stop doing that, and then we can build something together, with your new Lego (something he really likes doing), or you can carry on, and you will have to go and sit by yourself (something he hates doing).
Whatever choice your child makes, you HAVE to see the choices through, as soon as they make their choice.
This is a calm way to deal with unwanted behaviour, and they will quickly learn that they prefer the nice choice.