There are so many things, but something I found recently is meditation, mindfulness and to ground yourself in the now. It sounds super hippie, but it really works.
This is a pretty good podcast that touches it with Duncan Trussel:
http://duncantrussell.com/medicine-space-with-aubrey-marcus/#/vanilla/discussion/embed/?vanilla_discussion_id=0Exercise is an other thing. I can not stretch this enough. It makes you happy like a switch that turns it on.
I have had super ****ty days, maybe a fight with my wife, but after a good workout all the problems are completely gone and you call home and apologize for the stupid **** you said.
I recommend finding a way of exercise you think sounds interesting, get a program of some sort and stick to that for at least 3 months before trying something new. I love calisthenics and power lifting, but think about what kind of person you are and what might suit.
Music.