Julia Scott, who blogs at Bargain Babe, suggests another tactic: hesitation. She recently selected something on a shopping site but clicked off without buying. A few days later the merchant e-mailed a coupon code to encourage completion of the deal.

Incidentally, a few companies won't allow you to combine cash-back shopping with discount codes. Most will, but you should use only codes provided on the cash-back site. Otherwise, you probably won't get credit for the purchase.

Sale + coupon = big savings

Want an even better price for that cashmere sweater or fishing lure? Sign up for "deal alerts." Note exactly what you're looking for, and the discount site will e-mail you if the item goes on sale. The shopping code makes the deal even sweeter.

Many online discount sites offer weekly "hot deals" newsletters. Your favorite merchants probably do, too, and additional discount codes are often included. Sign up for both, but start a separate account for shopping-related e-mail. You'll get a lot of it.

Kyle James of Rather Be Shopping says members often use price-aggregator sites such as PriceGrabber.com or BizRate to find the best prices. After that, they check Rather Be Shopping for discount codes to match.

Mary Wazelle, who lives in rural Minnesota, does it the other way around: She goes online to find top coupons (her best to date is 60% off), then decides where to shop.

"I like the thrill of the hunt," Wazelle says. "I even buy shampoo and toilet paper online." Internet purchases also keep her from having to drive 35 miles to the nearest shopping area.

Should you find a hot shopping code or an amazing clearance sale, don't delay. Some of the really smokin' deals last for 24 hours or less, and merchants have been known to pull coupons or change their terms without warning.

"If you are ready to buy when the deal is there, that's when you will save (the most)," says Jeni Putalavage-Ross, a spokeswoman for couponSeven.com.

Do the math

Generally, you have to choose between free shipping codes and percentage/dollars-off codes. Few retailers allow you to use both at the same time.

Free shipping is often the better deal, but not always. For example, jewelry weighs so little (and can cost so much) that a percentage/dollar-off coupon is the smart choice.

Besides, more retailers routinely offer free or low-cost shipping. Arizona resident Jami Hagen used a 20%-off coupon to buy pool umbrellas on end-of-season clearance from Overstock.com, a company with a $1.95 shipping deal at the time (the price has since gone up to $2.95). She wound up paying $50 for two umbrellas that normally cost $129 apiece.

Hagen also favors apparel retailer Lane Bryant, which lets her stack discount and free-shipping codes along with "coupon checks" from the company's catalog. These discounts plus clearance prices have allowed her to buy as many as 15 items for less than $20.

"It's amazing, the things you can find," says Hagen, a teacher and mother of three. "Those of us on budgets, we have to shop this way."

Certain companies offer free "site-to-store shipping," yet another way to sidestep delivery charges. You order online, using the best percent- or dollars-off code you can find, then specify the purchase be shipped to the brick-and-mortar location in your area.

Ginger, a reader who lives near Buffalo, N.Y., bought four appliances this way. Three were from stores that offered free local delivery, so she and her fiancé had to pick up only one item.

"Anytime I'm purchasing something online I do coupon codes," she says. "I like money. I want to keep as much of mine as I can."

Site-to-store shipping is a particularly good choice for working folks who won't be home to accept delivery. Some drivers leave packages at the front door, which not only invites theft but also signals to potential burglars that no one is home.

Tips from the pros

Online discount codes can mean considerable savings, but only if you use them right. Here are tips to keep in mind:

• Codes are free. Avoid any site that tries to sell you a "membership."
• Be a fan. Merchants offer exclusive discounts for Twitter and Facebook followers, according to Sara Dunham of Savings.com.
• Have backup codes ready. Sometimes a discount has expired.
• Check shipping options. Tricia Meyer, owner of Sunshine Rewards, found it would cost only $2.50 to have four video games sent via regular mail versus private carrier. She chose to use the 20%-off coupon and wait a little longer for delivery.
• Shop out of season. If long-sleeved women's shirts are $2.99 in May, buy half a dozen for next fall.
• Check totals carefully. Maybe you misspelled a code, or maybe it expired. Make sure that the discounts were applied before you click "place order."

Donna Freedman is a freelance writer in Seattle. You can find more of her writing on MSN Money's Frugal Cool blog and at Surviving and Thriving (motto: "Life is short. But it's also wide.").