I think the key to worry less and be happier is to always keep in mind everything happens for a reason. Sometimes bad things happen and we don't know why. We think everything is falling apart or this is the end of all good things, but the truth is we can't see the whole picture. Everyday of our lives is just us unraveling a piece of it. Everyday we see things a bit more clearer, understand the world a bit more. We become wiser, smarter, and better in so many ways but there's still so much that we don't understand and maybe we can't understand for a while but one day we will. One day everything good and bad will make sense. You'll realize that you didn't get a certain opportunity because a better one was on the way, or that someone you loved left you because you'll meet someone that will love you even more, or that all the hardships you go through are just a key you use to unlock the better parts of your life. So many things are a mystery to us right now but it won't be that way for long. You just have to trust God because he knows the big picture. He knows what's best for you and what's not and He loves you and protects you. Keep all of this in mind and you'll realize how less stressful your life will be and how happier and more content you will be.

Eventually all things fall into place. Until then, laugh at the confusion, live for the moments, and know everything happens for a reason.
— Albert Schweitzer