figure out what the little things that don't matter are and just let them go....
my first real job was a mangager at a pizza place. i used to get real upset if a pizza burned or had to be re-made. so this guy i worked with used to say "don't worry, it's just pizza. no body's gonna die, just let it go."
so any time something is bothering me and i know that it really just doesn't matter , i just say to myself " it's just pizza, let it go!"