I think that one very useful tool in mastering your emotions is simple patience. Having the patience to think things through, let your mind do it's work and wait for it to arrive at the "right" response is the key to avoiding rash decisions and for understanding the big picture behind the situation that created the emotion in the first place.
Check out
this smart-kit.com article for the wisdom behind the expression "sleep on it." This is why I say to wait for your brain to arrive at the right conclusion, rather than forcing a response that might not be right for the situation.