The recipe for saving money at the grocery store is simple—it’s all about preparation.

“The key is planning,” says Stephanie Nelson, founder of The Coupon Mom (Couponmom.com), an online coupon-management program. “You should sit down with the grocery store circular and see what’s on sale that week, and then plan your meals and prepare your grocery list.”

Nelson believes that the best way to save money is by staying out of the store. The average person makes three trips to the store per week and is likely to spend more than anticipated during each of these trips.

If you want to save money, Nelson says, you should hit the store only once a week.

“Despite being strapped for time and trying to stretch a dollar, most people just rush to the store when they have a free minute,” observes Melissa Lederer, senior vice president of marketing for CoolSavings.com, a website that offers consumers coupons and free samples of products. “They don’t make a list, don’t have their coupons at the ready, and aren’t familiar with the store’s weekly sales promotions, and so are likely to spend more money.”

Both Nelson and Lederer believe that the best way to save money at the store is by using coupons.

On the low end, “the average family of four spends over $6,000 per year for groceries. I don’t think it is unrealistic that a family could save up to a third of its food [budget] by using coupons and taking advantage of other special sale programs,” says Nelson.

To Nelson, not using coupons is like throwing money out the window. “If you saw a dollar in the street, you’d pick it up, but 99 percent of all coupons are thrown out,” she says.

Here are some other quick tips from Couponmom.com and CoolSavings.com for saving at least $25 per month at the grocery store—and maybe even per trip:

1. Steer clear of prepared foods. Buying vegetables that are already cleaned and cut will save time but will cost more. Fish or meat that is preseasoned can cost an additional several dollars per pound.

2. Don’t shop for groceries when you’re hungry. You’re likely to be tempted to buy things that aren’t on your list. If you’re shopping with kids, be sure to pack snacks and treats so they don’t hit you up at the candy aisle.

3. Double up on double-coupon days and take advantage of other stores’ coupons. Many grocery stores offer double-coupon days, will match competitors’ prices and will accept competitors’ coupons. So even if you’re loyal to one store, you can still take advantage of the sales promotions at the other stores in your area. Make sure to ask about your favorite store’s coupon policy.

4. Look elsewhere for other valuable coupons. In addition to looking for coupons in your Sunday newspaper, check out your favorite manufacturers’ websites. Manufacturers like Procter & Gamble (PG.com) and General Mills (GeneralMills.com) offer their own special savings.

5. Don’t assume store brands are the best buy. While generic brands are often less expensive, some stores have created pseudo-luxury brands. Don’t put the item in your cart until you’ve compared the price per unit for the various brands.

6. Speaking of which, make sure you do the math. Always shop with a calculator so you can easily figure out price per unit or price per pound and what you’re truly saving.

7. Don’t assume bigger is always better. Sometimes the bigger bag or can will actually cost more per ounce than its smaller counterpart. Dig out that calculator and compare price per ounce.

8. Don’t assume your grocery store will have the cheapest prices for cleaning, drugstore and personal-care products. Typically, cleaning and personal-care products cost more at grocery stores. However, if you have coupons and the grocery store is offering a limited-time buy-one-get-one-free promotion or other special program, it may be cheaper to buy the item there than to purchase it at a discount store—especially if you have to travel 10 miles each way to get there.

9. Don’t get suckered into buying more than you need or can use. If your grocery store is offering a “10 for $10” promotion, you don’t need to buy all 10 peaches, plums or lemons to receive the sale price. You’ll get the prorated price even if you buy only two or three of the sale items.

10. Cut back on waste and save even more. According to the USDA, consumers throw out anywhere from 5 to 20 percent of the groceries they purchase. Remember, it isn’t just about how you spend money at the store. If you truly want to save money, you’ll have to manage the food you buy economically at home.