First of all, happy people live in the present and avoid worrying about the past and the future. This is a yogic perspective but it's also just a good way to live. We cannot control what happens in the future and we certainly cannot control what has already happened. All we know for sure is the here and the now. And if you can't enjoy the present, what's the point?
Happy people don't let desires rule them. Instead of thinking that they need this or that to be happy, they're content with what they already have. The planet benefits from this sort of happiness, because it promotes anti-consumerism. You don't need to buy, buy, buy to be happy.
Attachments degrade happiness as well. Yes, you may enjoy a cup o' Joe in the morning, but if you don't have it you're not going to turn into hell on wheels. And you love to meditate and do yoga in the morning, but if you miss a day, it isn't the end of the world. It's about being flexible and willing to take what comes at you without creating stress and tension.