Spend Some Quality Time in Your Closet
Become familiar with what you have, how you wear it and what styles look great on you, then let that knowledge inform the purchases you make.
Assess Your Needs
Come up with a list of what you need in order to get the most wear out of what you already have. Also look for gaps in your wardrobe—for instance, are you lacking a go-to dress for special occasions? And if an old favorite is starting to show its wear, start looking for a replacement soon.
Think Like a Fashion Stylist
Create a Pinterest board and upload photos of items that you own and like but that you want to pair with something new, such as a full skirt that needs just the right fitted top. Also collect images of purchases you're considering and outfits that inspire you. When you're in the stores, refer to the Pinterest board on your smartphone to help you keep focused. Or, try a wardrobe-organizing app such as Stylebook ($4 on iOS), which allows you to catalog what you own, arrange pieces into outfits and incorporate items that you're considering into your current wardrobe (so you can see how they work with what you have).
Know When to Splurge
Basically, it all comes down to cost per wearing. For instance, a winter coat that sets you back $100 and lasts only one season is not as good a buy as one that costs twice as much but lasts three seasons.
Wear the Right Shopping 'Uniform'
Trying on clothes can be exhausting, but it's necessary. To make things easier, wear comfortable clothes that are easy to slip on and off, such as leggings and a T-shirt.
Don't Buy Fixer-Uppers
Unless you're a seamstress, put items that need a nip or a tuck on the discard pile. Except for hemming, alterations by a tailor tend to be expensive.
Know When to Scrimp
Finally! When You Get Your Haul Home
Try it on again. Now that you've unloaded the car, try on each piece with items you already own so you can see whether it does, in fact, work with your wardrobe.
Put it away. Hang your new item, or fold and place it in a drawer—but don't remove the tags! Make a note in your calendar of the latest return date, with a reminder set a week before; if you haven't had the urge to wear the same piece by then, consider taking it back.
Save your receipts. You'd need them to make a return, and if the item gets marked down, you might qualify for a price adjustment. Make it easier with an app such as OneReceipt (free, iOS), which organizes e-mail receipts automatically.