I use different methods depending on the source of the anger, and on my daughter's mood.
* a time-in : big hug, or simply sitting beside her, and staying quiet
* labeling feelings, helping them learn the physical side to anger - ie clenching fists
* deep breathing - or count to 5
* painting, or drawing, or cutting up paper, or smashing playdough - expressing the feelings through art - even the motions and colors they choose can help get the angries out
* play pretend - with dolls or toys - role playing for little ones - re-enact the situation that caused anger
* make an object the guilty party - ie. angry/frustrated can't pull down her pants - say that those pants are held on so tight - and say let go pants, ect. silliness helps a lot
* make sure your child witnesses you dealing with your feelings - and if you usually yell, so will your child.
There are more ways I use, but each depend on specific situations. Hope these help