Here are a few pointers:
Happiness isn’t about getting all the circumstances of your life “just so”.
Of course, there are many different ways of understanding happiness. But if you expect to get to happiness by tweaking your life to get rid of the things you don’t like and fill it with things you do like, you’ll never be happy. There’s a happiness that doesn’t depend on how well things are going around you, or even on emotions. Sadness isn’t the opposite of this kind of happiness. It doesn’t really have an opposite. It doesn’t depend on anything. You don’t have to make it or go out and get it. It’s already there. You just have to recognize it.
Get out of your head.
If you pay careful attention to what makes you feel unhappy, you nearly always discover that there’s some form of thought at the bottom of it. Often, it’s a thought about how much better things would be if only…(fill in the blank). Or about how how reality isn’t living up to some expectation. Or about how your dreams keep getting squashed. Or about how you dread doing this or that. Wallowing in thoughts like these can make you feel pretty miserable. You can’t do much about keeping stuff like this from bubbling up, but you can definitely decline to do the wallowing thing. Instead of playing this game of comparing reality to some imagined alternative, open up to what’s there. Engage with this world and find its beauty.
Reach out to others.
Make connections. This doesn’t have to be dramatic or complicated; it can just mean opening your shell enough to in some small way make someone else feel less alone.
Perhaps you can see that all of these are related. They’re all just ways of saying “get out of yourself and embrace life just as it is”.