The notion that money can't buy happiness is one of those things everybody claims to believe, when in reality surely no one does. It's true that winning millions on the lottery seems to leave most people more miserable and unpleasant, or unchanged at best. But who isn't convinced that the situation would be different if they won? Indeed, research shows there's a link between income and wellbeing, not just because poverty is depressing, but because even if you're well-off, becoming more well-off has a small positive effect. The question isn't whether money can buy happiness; to a limited extent, it can. The question is how.

A case in point: recently, I received £800 I hadn't planned on receiving. (International arms smuggling is such easy money.) In the past, I'd have deposited it in a current account; a few months later, it'd be gone, and I'd be living just within my means, as always, with nothing to show for the extra cash. This time, I wanted expert opinions on spending it for maximum happiness, which led me to Sonja Lyubomirsky.

Lyubomirsky is a psychologist at the University of California, and I fervently hope that her excellent new book, The How Of Happiness, doesn't get lost in the several thousand titles on this topic published every six minutes. She's the first of the "positive psychologists" with solid research credentials to drop the sniffy aversion to self-help, resulting in a work that's simultaneously practical yet grounded in her team's studies. Mostly, it's not about money; its role, Lyubomirsky concurs, is minor. But one of her recurrent themes is highly relevant to money: in happiness, variety is everything.

Anything that becomes too much of a fixture seems to lose its power to cheer us. In experiments, people asked to keep a gratitude diary get happier - but more so if they do it weekly, not daily. People asked to perform a certain number of acts of kindness per week feel better if they group them on one day, or vary them; the same act, done daily, doesn't improve mood. We think a new car or kitchen will thrill us; instead (thanks to "hedonic adaptation", previously mentioned here) it becomes the norm. So, Lyubomirsky concludes, "If you suddenly experienced a financial windfall, you ultimately would be much happier if you spent the money on numerous pleasant, mood-boosting things, occurring on a day-to-day or weekly basis." Mostly, she implies, these things should involve social connection, a far more reliable source of pleasure. I should probably spend my £800 on going places with friends.

But a little materialism might have a role. We think of our society as materialistic, but as the philosopher Alan Watts liked to note, obsession with money isn't materialism: it's "abstractionism", a preoccupation with a symbol. True materialism - relishing the immediate and physical present, which might include a new iPod, good food, or clothes - is the opposite, and not bad.

I'll let you know what I do with the money. Right now, I'm happiest not deciding.

oliver.burkeman@theguardian.com