Misery: it's everywhere these days. We are all popping happy pills like Smarties, checking ourselves into the Priory and stocking up on happiness books. But for every report telling us it is all down to our ever-longer working hours, additive-laden food and endless commutes, there is a growing body of scientific research suggesting that happiness is, quite literally, a state of mind.

"You have to decide to be happy," says Paul Jenner, author of Teach Yourself Happiness. "Most people think happiness is something that arrives by itself, like rain. But it isn't. Barring seriously depressed people, most westerners have plenty to be happy about, but they choose to focus on things they haven't got. It really is that simple."

Scientific research is starting to back this idea up. Rather than happiness being something we earn through circumstances, it seems we can work at it in the same way we work our bodies at the gym, reaching beyond our "genetic set point", the predisposition to happiness (or unhappiness) we were born with.

According to Sonja Lyubomirsky, psychology professor at the University of California, Riverside, who has been researching happiness, there is converging evidence that some people are born happier than others, but that all of us can learn from their habits to raise our own happiness levels.

How do we do this? By adopting certain exercises - or "happiness strategies"- that Lyubomirsky, in her tests, found very effective in perking people up.

"People born with a high set point will do these 'happiness strategies' automatically, and we all know people like that - they naturally look on the bright side and are good at maintaining relationships - but if it doesn't come naturally, we have to work at it, in the same way someone who is genetically determined to be overweight has to watch their diet and exercise."

This issue of "working at it" is crucial to Lyubomirsky's approach. She has discovered that timing and persistence are crucial. Do the exercises too often, and you may get bored; don't do them often enough, and they may not make a difference.

So can a negative person really become happier through adopting these strategies? Lyubomirsky thinks so. "If you work at it, it becomes a habit. Something I want to explore in the future is whether the exercises can become so habitual that we automatically begin to think in more positive ways."

The first thing to do is step off the "hedonic treadmill": that constant hunger for new acquisitions and experiences, which is seductive but which leaves people ultimately dissatisfied and hankering for more. "The hedonic treadmill is one of the major barriers to happiness," says Lyubomirsky. One way to counter it, she says, is to invest meaning in goals that we adapt to less easily, "things that challenge and surprise us", rather than static things such as money and possessions. "Because if you adapt to everything positive that happens to you, how can you raise and maintain your happiness levels?"

Lyubomirsky calls goals "dynamic happiness strategies": they are things such as learning a language, taking up exercise, trying to be more forgiving, or focusing more on spiritual or philosophical beliefs (well-known happiness-boosters).

No-nos include comparing ourselves to other people and negative rumination ("in a way that doesn't problem-solve"). "Research shows that constant rumination on negative events is linked to depression. If you are mildly depressed, it will depress you even more," she explains.

Can moaning ever be useful? Perhaps, says Nicky Page, from the UK Centre for Applied Positive Psychology, citing research that in order to be a "high-performing team" you need three positive interactions (approvals) to one negative interaction (disagreement). "The point is that you need that negativity, otherwise you become a back-slapping loop that can't look at itself objectively."

What most psychologists agree is that putting our thoughts into writing is useful. "Writing about your goals gives you an opportunity to learn about who you really are," says Lyubomirsky. "It helps you see the 'big picture' of your life" ·

Five ways to lift your mood

1 Make a note of three things that went well today, and why

This exercise, devised by former president of the American Psychological Association, Martin Seligman, proved so powerful that it helped to launch the Positive Psychology Movement. What Seligman found was that this exercise, above all others, had a significant effect on treating depression, comparing favourably to anti-depressants and psychotherapy.

Psychologist Robert Emmons, from the University of California at Davis, found it improves physical health, energy levels and, for patients with neuromuscular disease, relieves pain and fatigue. One study found it worked better if it was done weekly instead.

2 Identify your strengths and every week, aim to use them in new, creative ways.

"This exercise gives a huge boost," says Page. "It significantly increases people's wellbeing and makes them feel more engaged at work ... One study showed that the average person uses their strengths only 37% of the time, while 'highly engaged individuals' use them for more than 70% of any given week." Identify your strengths by taking a free test (try viastrengths.org) or asking friends.

3 Imagine and write about your best possible self in 10 years' time.

"This is an optimism exercise," says Lyubomirsky. "It leads the person to consider their life dreams, boosts positive thinking and enhances self-regulation." Psychologists have long known that optimism is a good buffer against unhappiness, as well as being associated with longer life and good physical health.

4 Write someone a thank-you letter.

If there is someone you are grateful to - a friend, a mentor or a parent - once a month write a 300-word thank-you letter and, here comes the yucky part, deliver it personally. Better still, read it aloud. Seligman found people who do this just once are less depressed and happier a month later. Three months later, the effect was gone - so you have to repeat the exercise.

5 Commit five acts of kindness a week.

It can be anything from helping an elderly neighbour with her shopping to babysitting. Interestingly, people told to vary their good deeds ended up happier than those who felt pressured into being kind all the time. Why does altruism give you a lift? Psychologists say it makes you feel generous and capable, allowing a greater sense of connection - all of which make life a more pleasurable place.