This year, a few pure souls might celebrate a freegan Christmas. Some will opt for a "Buy-Nothing" holiday. Others still will pull off a DIY Hanukkah.

The vast majority of people who have some disposable income, however, will do what all the glossy store catalogs implore this time of year and "SHOP NOW." Even among those who think that Black Friday insanity, and holiday consumerism in general, are terrible, the default setting during December is to buy things.

Behavioral economists have been puzzling for years over how much and what kinds of spending provides the biggest happiness boost for the buyer. But it turns out that whether people reap good vibes from their purchases depends on much more than how many sweet deals they snap up or how much Uncle Ron likes that new armadillo beverage holder.

In 2011, Elizabeth Dunn of the University of British Columbia, Daniel Gilbert of Harvard, and Timothy Wilson of the University of Virginia sought to figure out how to shop in a way that optimizes happiness, based on the notion that most people misunderstand what will "make them happy, how happy it will make them, and how long that happiness will last."

They came up with eight such rules, which they described in a paper with the delightfully capitalistic title, "If money doesn't make you happy, then you probably aren't spending it right."

1) Buy experiences, not things: This is a well-documented principle. Adventures make stronger and longer impressions on our brains than new boots do. Or as the authors eloquently put it, "After devoting days to selecting the perfect hardwood floor to install in a new condo, homebuyers find their once beloved Brazilian cherry floors quickly become nothing more than the unnoticed ground beneath their feet. In contrast, their memory of seeing a baby cheetah at dawn on an African safari continues to provide delight."

2) Help others, not yourself: Because humans are so profoundly social, studies show that people across cultures are happier when they spend money on other people, rather than themselves. So go ahead and buy that expensive scarf, but give it to your sister.

3) Buy lots of little things, rather than one big thing: People adapt to having new stuff, and anything that disrupts that adaptation is likely to prolong happiness. Just as you start to get used to that one new blouse, up comes another one. As the authors explain: "Having a beer after work with friends, for example, is never exactly the same as it was before; this week the bar had a new India Pale Ale from Oregon on tap, and Sam brought along his new friend Kate who told a funny story about dachshunds. If we buy an expensive dining room table, on the other hand, it's pretty much the same table today as it was last week. Because frequent small pleasures are different each time they occur, they forestall adaptation."

4) Don't buy the warranty: Remember that time you cracked your iPhone, and you thought you'd go back to the Apple store for a replacement right away, but instead you just kind of used the cracked one for another four months until the new version came out? And it was pretty much fine? People adapt to good things, the psychologists write, but they adapt to bad things, too. The "psychological immune system" will find a way to spin the iPhone accident positively. (At least the cracked one is less likely to get stolen, our internal Pollyanna might say.)

5) Buy now, consume later: Not only does this principle help build anticipation—another happiness driver—it also foments uncertainty about the reward and helps us make better, more future-oriented choices. It's a good thing Christmas, with its presents sitting under the tree for days, has a built-in delayed gratification mechanism.

6) Consider the details: Much of our happiness is determined not by big life changes, but by the annoying little hassles (or tiny "uplifts") that pepper our days. "Consider the choice between a small, well-kept cottage and a larger 'fixer upper' that have similar prices," the authors write. "The bigger home may seem like a better deal, but if the fixer upper requires trading Saturday afternoons with friends for Saturday afternoons with plumbers, it may not be such a good deal after all."

7) On the other hand, don't comparison shop: Spending too much time digging through Amazon reviews can lead to over-thinking purchases and obsessing over factors that don't really matter. In one experiment, when study subjects were presented with a choice between a larger chocolate valued at $2 that was shaped like a cockroach and a smaller chocolate valued at 50 cents that was shaped like a heart, only 46 percent said they would enjoy the cockroach more. But 68 percent said they'd choose the cockroach. Sometimes, shopping around nudges us to choose the better deal, despite what we actually prefer.

8) Follow the herd: People sometimes enjoy things more simply because others like them, which explains the popularity of "hot" yoga and other tortures. Here, the authors quote the 17th century author François de La Rochefoucauld in saying, Before we set our hearts too much upon anything, let us first examine how happy those are who already possess it.

The psychologists conclude that, "Money can buy many, if not most, if not all of the things that make people happy, and if it doesn't, then the fault is ours."

If this Rational Actor Christmas is not merry, in other words, you have only yourself to blame.

For more on how to apply these rules, read Derek Thompson's interview with Gilbert here.