The first thing you could do is choose the right parents.
Not so you would inherit a bazillion bucks but so you could inherit a high set point for happiness. Research has shown that people are genetically dispositioned to have a set point that keeps their happiness within a range.
It's not quite as simple as saying people are born happy or unhappy, but rather that people have a tendancy towards one or the other. We all know people who are naturally upbeat, happy and see the glass as half full. Conversely we all know people who are downbeat, unhappy and see the glass as half empty.
Studies have shown that people who win the lottery and people who lose a limb - will after time, return to about the same level of happiness they started at before those events. What does that tell you?
It should tell you that externalities are not going to make you happy or unhappy. You have to work from the inside out. You choose your attitude regardless of the situation you find yourself in. I'm going to assume for the sake of argument that people want to be happy and want the people around them to be happy as well.
The good news is that you can move your personal happiness quotient higher within your range with some simple advice -
Maintain ties with family and or friends. Foster relationships. People who are in contact with other people are not only happier but healthier as well.
Get some exercise. No matter what kind of physical activity you choose - do something. Walk, bike, garden, mow your lawn, swim, climb stairs...anything that gets you moving.
Eat healthy foods. It is true that you are what you eat. Eat foods that are high in fiber, low in added sugar (especially the all pervasive high fructose corn syrup which adds extra calories to so much food...you really don't need sugar in your canned soup), look for natural unprocessed foods - avoid eating things that your grandparents wouldn't recognize as food.
Drink plenty of water. It's easy to get dehydrated and not even know it. The symptoms can be headaches and low energy.
Get enough sleep. Relax, take a nap when you are tired.
Practice meditation of some sort. The left frontal cortex has been shown to be active in people who are happy. The people who have the highest activity in this part of the brain turn out to be those who practice meditation. It doesn't have to be a big deal - straighten your back, turn down the external noise, take some deep breaths and watch your thoughts flow by without trying to hold onto any of them.
There's a bit of a catch 22 here though, if the only way to be happy is to be born happy and through the luck of the draw you got the unhappy genes, your natural tendency may be to choose a really bad attitude, and make yourself as well as those around you miserable. I'm not really sure there's much that can be done besides taking the advice already given - stay close to family and or friends, exercise, eat right, drink water, get enough sleep, meditate...but what do I know. Anyone who is clinically depressed should seek professional help - those professionals can help you get back on the path.
One last thing - it's a mistake to think that our goal is to be happy as a steady state condition. We should treat happiness like a direction on a compass - you want to be in tune with your mind and body enough to know when you are heading in the right direction (towards happiness). Your happiness will fluctuate - that's normal - sometimes you will be off 180 degrees and start getting really unhappy - when that happens turn around, take a different path, and if all else fails stop and ask for directions.
