1. Never shop when you're hungry. Everything looks good then and you're more inclined to bring home too much junk food or too much or whatever you're hungry for. "Too much" means that it can spoil before you can eat it. It could mean that your grocery budget will be too short to cover the rest of the food you need later. It can also mean that you buy more than is nutritionally good for you to eat. One candy bar may be ok, but a dozen can break your budget as well as your health.
2. Shop alone whenever you can. That way you can control what you buy. Spouses, children, parents and friends all have their ideas of what they think you should buy. If you're buying for your family, of course take their tastes into account, but when you shop by yourself, you can find ways to minimize extra costs in various ways. For instance, you can buy ingredients to make their favorite food from scratch rather than buying ready-made.
3. Make use of coupons only when they make sense. Don't automatically assume that they will get you the product cheaper than any other way. Keep an eye out for sales, compare generic to brand name and then consider coupons. You may be surprised to find that some regular generic prices are less than brand name with coupons.
4. When food is cheap, buy as much of it as you can, then dehydrate, freeze or can it for later use. Around Thanksgiving, turkey is cheap: buy an extra for later. At Easter, traditional hams go on sale, St Patrick's Day means corned beef; Lent means fish. Summer time is good for stocking up on various vegetables and fruits, late summer and autumn brings squash and pumpkins. Pay attention to seasonal fluctuations in prices and you can save by not buying them at their highest.
5. Never shop with your eyes on the most convenient section of the shelves. Look high and look low. Grocery stores know that we are too lazy to stoop down or stretch up, so the highest priced goods are within an easy reach. Watch out for "end cap" sales, too. Sometimes they are real sales and sometimes, not. Occasionally, you will come across a really good, unadvertised sale, so keep your eyes open.