I'm noticeably happier now than I was a few years ago, and the reason is that I stopped doing things that didn't make me happy and started doing things that did make me happy. It was surprisingly hard to figure out what brings about lasting happiness.
Through a process of internal investigating (meditation) and systematic experimenting with new behaviors (volunteering, charity, listening, letting other people go first, confronting fears, letting go of material attachments, etc.), I learned something that is worth sharing:
Anything that makes you happy and also makes others happy will lead to lasting happiness.
Something that makes you happy at the expense of others, or something that makes others happy but not you, will not lead to lasting happiness for you. This is to say that lasting happiness is not to be found in the pursuit of self-gratification, nor is it to be found in the pursuit of selfless sainthood. Happiness is to be found in the middle, where you create situations that benefit yourself and others. To put it another way:
Happiness is a collaboration.
The good news is that anyone can find happiness this way. The "bad" news is that, if you've spent your whole life until today pursuing self-gratification, then you should expect that it will take a lot of effort to climb out of the emotional hole you've been digging. Even so, it doesn't take long before you begin to enjoy the process of climbing.
If you do try it out, I think you'll be happy with the results.