If you want to make the single biggest improvement in your life possible, here it is in a nutshell:
Figure out the difference between what you're able to control, and what you can't control. Then, don't stress out over what you can't control.
Otherwise, you're the idiot screaming at a steering wheel on the verge of a stroke while you and everyone else around you wait in a 4 lane traffic jam. That's fighting a battle you can't win.
I can't lie to you, this took me forever to learn, and I still have my bad days. They're increasingly few and far between. However, where's what I've learned: Once I started reaping the benefits of not sweating the stuff I can't do anything about, my life got a whole lot better. Not just a little bit better, not just a minor improvement. There is a huge difference in my stress level and my general happiness.
Figure this out, you're well on your way to winning whatever battles you have to fight.