Every day, focus on and take pleasure from things that are simple or free: birdsong, sunrise and sunset, the shape of clouds, dogs zooming across the park, the shifting seasons - flowers, baby ducklings, autumn leaves, frost. There's so much beauty all around.
Take pleasure in things you already have in your life, and pay more attention to them: the taste of fresh tea or coffee in the morning, clean sheets, listening to a favourite song, reading a good book in the bath or curled up in bed.
Make small changes - they give you a fresh outlook - move the furniture around sometimes, or put different clothes together to create a new outfit from your existing wardrobe.
Do things you want to do but put off for no good reason. A life-long friend of mine became a poet who often performed in the town where we grew up. I always meant to go to one of his readings but it was a long way to travel and we'd sort of lost touch, so I didn't. Then he died unexpectedly young. The first time I heard his poems were at his funeral. They were brilliant and I wish I'd been able to tell him that in his lifetime. After the funeral, I made plans to meet up again with old friends instead of putting it off and now we see each other regularly.
Also, I really am not happy all the time. A lot of the time I have post-menopause meh. But I do try to keep returning to the small, easy ways to find happiness.