Claims, Insults, Supporting Rebels

Claims
In order to take the most provinces out of a war you should make claims on the lands of your enemies. It also reduces % at which independence rebels grow in those territories.

Insults
Usually less common diplomatic action. Gives the person you insulted a casus belli. Apart from that it does little to help you.

Supporting Rebels
Next up is supporting rebels. Useful tool if you have a lot of spare gold and someone you don't want to expand.Depending on your ideas this can make a pretty big impact in the lands of your enemy.