Just short of a reward ticket? T+L’s tips on the best ways to earn—and spend—frequent-flier miles.

Airlines once awarded frequent-flier miles to win loyalty. Today, carriers are selling miles, making them one more stream of revenue, much like checked bags and blankets. Most programs claim passengers can score round-trip tickets for only 25,000 miles, but seats at that rate are limited, so it's important to manage your points carefully.

Plan ahead. Miles from online retailers and bonus offers can take weeks to post to your account.

Shop online—wisely. Check your frequent-flier website before doing any online shopping. Most programs have portals that award from one to 25 miles per dollar spent at popular retailers such as Nordstrom, Pottery Barn, and Best Buy.

Use miles for upgrades. If there’s a fare sale to your desired destination, you may want to pay out of pocket for an economy seat and use your miles to upgrade to business or first class. You’ll save on checked bags, meals, and other extras such as headsets and pillows.

Buy miles only as a last resort. Purchasing miles is expensive (about 2.7 cents apiece). Instead, wait for a sale or bonus offer, and, if possible, use your mileage-awarding credit card to earn extra miles on the purchase and any fees or taxes.

By Jennifer FlowersJennifer CooganNicholas Teddy and Jennifer Coogan