The other day an e-mail from Old Navy arrived in my in-box with the subject line “Buy one, get one 50 percent off all activewear. Two days only!” I get these sales e-mails from the store almost weekly, and even though I know exactly what the marketers are doing (trying to get me to spend money I wasn't planning to spend), I usually click—and often end up purchasing—anyway. As a mortgage-owing, self-employed mom with two college funds and a retirement account to think about, I have got to become a smarter, better shopper. You, too? Here's how consumer psychology and marketing researchers suggest we start.

#1 Know that scarcity can sway you—big time. That Old Navy e-mail used a really compelling tactic by highlighting the limited time parameters of the sale—it introduced the idea of scarcity into readers' minds and implied that we could miss out. “Scarcity is very primal,” says Kelly Goldsmith, assistant professor of marketing at the Kellogg School of Management at Northwestern University. “When people see the world as running out of anything, the research shows it makes them crazy selfish—it starts to explain things like Black Friday violence.” If something's scarce, our minds tell us it is valuable and we need to snap it up. Even if we really, truly don't.

#2 Prioritize before you shop around. The other week it took me three hours to decide which local hotel to book for an overnight staycation. There were just so many; what if I picked the wrong one and my husband and I ended up having a terrible time? This quandary illustrates one of the biggest problems facing shoppers these days, says Alexander Chernev, a consumer behavior researcher and marketing professor at the Kellogg School: too much choice. “It takes a lot of effort just to consider all the options available—to go out and find them and evaluate each one,” Chernev notes. He points out you don't have to consider all the options, especially if you start with a good sense of your priorities: “You always have to give up one thing for another. Do you prefer better coverage or lower price in health care? In buying a car, do you prefer performance, or comfort, or fuel efficiency?” If you figure out what's most important to you ahead of time and consider only the options that match your priorities, you can keep from foundering in a sea of too many choices.

#3 Make a list—even online. Making a shopping list before hitting a store isn't just about remembering necessary items, it can also help you tune out unwanted marketing messages. Studies on goal activation show that if you make a concrete action plan (such as a shopping list), you're more likely to do what it is you actually set out to do. “Imagine your average trip to the grocery store,” Goldsmith says. “We go with good intentions, to get our bread and milk, then we're bombarded by in-aisle displays and coupons that are meant to arouse us or change our minds about what we actually need.” Although carrying a list may seem like a no-brainer when heading to the store, Goldsmith points out that a shopping list can help just as much online, where banner ads and pop-ups try to entice you with complementary products to those in your cart. A shopping list can keep your goal of shopping wisely at the top of your mind amid all these distractions.

#4 Try to think longer term. In the moment, it can be tough for shoppers to balance what consumer researchers call “vices and virtues.” A vice is anything that brings immediate gratification but costs you long term, whereas virtues may seem costlier now but are much better for you down the road. “In general, vices tend to prevail,” Chernev says. “If you think about how you're going to experience and enjoy the chocolate bar sold near the cash register, you're more likely to succumb.” One way to further boost your resistance to impulsive vice buys is to remind yourself of what you truly value in life. A series of studies in 2013 by psychologists Brandon Schmeichel of Texas A&M University and Kathleen Vohs of the University of Minnesota found that thinking and writing about your goals and values helped people exert more self-control when they were feeling run down or worn out. The next time I can't sleep and I'm tempted to fire up my Amazon app and buy a bunch of adorable baby clothes (on sale!) in the middle of the night, perhaps I'll grab a pen and paper instead and remind myself of what really matters.