I think the most simple advice I've ever received is that everything will be okay. That seems to be everybody's go-to pep talk line, and I have always rolled my eyes at the thought. Everybody has heard that line so many times that I think it's becoming (or already is, for that matter) irrelevant. That, however, is part of the problem.
What I've realized lately is that no matter how annoying it is to hear everything will be okay when you have totally convinced yourself that this is the end of the world as you know it, it's very necessary to tell yourself.
Nothing lasts forever. Not this stress you are feeling or that project you are working on at work or even most of the relationships in your life. Everything will be okay because everything eventually grows and morphs into something you never could have thought of before. I guarantee that when you think back to the last few years or so you would have never pictured yourself being where you are today or having experienced everything you have.
You're constantly growing and changing, and so are your situations.
Something to remember: even though everything is awful today doesn't mean everything will still be awful tomorrow.
You will pass that class without yelling at the kid behind you for smacking on their gum so loud it makes your cringe. You will pay that bill without having to sell your kidney's. You will finish that project without strangling your partner because you are strong enough, and everything will be okay.