When it comes to regulating your body and/or emotions, there is no one size fits all approach. What may help one person calm down, may actually cause another to increase their energy and vice versa.
Breathing Techniques
Yoga
Cosmic Kids has so many free videos to go through that range from a few minutes to up to an hour. Topics vary from animals to movies and television. Check out the video below for an introduction on mindfulness and yoga for kids.
Exercise (sometimes our body is craving a release so quick exercise helps!)
There are many brain breaks on youtube if you are looking for ideas. Danny Go is a big favorite around here!
Journaling (can be a drawing and/or writing journal)
Check out this article from Scholastic on how to get kids as young as 4 to journal
Distract
This is not a long term solution, but can be extremely helpful when helping to calm down.
Ideas include:
Boardgames
Cardgames
Reading
Having a snack
Taking a walk
Laying down
Mindfulness
Laying down and watching clouds go by
Blowing bubbles and watching where they fall without playing with them
Go on a walk (shape walk, scavenger hunt, color walk)