Good old ancient Greek advice still holds water.
If you think happiness is something that just happens to you, you have failed as a Greek philosopher. Even if Aristotelian philosophy (deeply feet-on-the-ground as it is) would not ignore the fact that there are certain things that lie beyond the human scope of action (as whether we like it or not, chance plays a role in our lives), what a good life is and how we can live life properly, is one of its central questions — and one that shouldn’t be understood in terms of luck, but rather of action.
Now, action is not supposed to be always heroic. In fact, your everyday Greek citizen would be concerned with not only heroism but also everyday, simple life, lived and thought of in broader terms. That is, quotidian life was considered to be (at least by Aristotelians) teleological. Put simply, saying life is “teleological” means life has an ultimate goal (the Greek word for it is “telos”) of its own, regardless of what we ourselves want to do with it. For Aristotle, such telos would be happiness. This means that even if we decide we want to be plumbers or horsemen, we want to be happy plumbers and happy horsemen, not cranky angry ones.
But happiness is not simply a feeling. The Greek word for happiness, “eudaimonia,” can be translated as “having a good spirit,” or “being in possession of a good soul.” This is where the Aristotelian genius kicks in. Having a good spirit would be the human equivalent of being a knife with a good cutting edge. You wouldn’t call a knife “good” if it’s unable to cut, simply because cutting is what a knife is for. So what is a human being “for”? If cutting is the proper activity of a knife, what is the activity more proper to a human being?
Aristotle would reply saying that, even if we share certain common features with plants and animals (we all eat, grow, and reproduce), what makes us distinctly and specifically human is our capacity to think. This rational part of the soul would be what we might consider the person’s “identity,” so to speak; what is specifically human in the human person. That is to say, that the activity proper to a human being is rational thinking. And rational thinking, translated in practical terms, implies virtuous action. In sum: just like a knife can be considered “a good knife” because it cuts well and effortlessly, a human being can be called “good” if he or she is living rationally and virtuously.
“Easier said than done, Aristotle,” we might reply, but Aristotle might well retort, “You know? It’s actually kind of easy.” It’s just a matter of building habits following one simple rule: when faced with two options, always choose the mean relative to you. That is, what is not excessive nor defective according to your own capacities. So, if you are a trained heavyweight boxer, then fighting Tyson might be the thing you’re supposed to do. If you are a ping pong master, fighting Tyson might not be the next best step in your career (so don’t try it).
This is prudence, according to Aristotle: the capacity to distinguish between excess and defect in every case, what allows us to distinguish courage from both rashness (excess) and cowardice (defect). Being at the crossroads between intellectual calculation (“what may be the mean specific to this dinner situation?”) and action (“I’ll go easy on the potatoes so I don’t stuff myself this time”), prudence is the key virtue that ensures happiness: it points at the mean between being wasteful or stingy (so we can be generous); boastful or self-deprecative (so we can be truthful); and obsequious or quarrelsome (so we can be truly friendly).
If you want to learn more about this classic approach to happiness, Aristotle’s Nicomachean Ethics is the book you need.