* All grocery stores have to get rid of certain items by the end of the day so if you plan to buy things like a whole cooked chicken(Chicken specifically gets marked down 3 hrs after cooking), go at the end of the trading day and you will find your chicken marked down, usually by less than even half-price. You can get a similar benefit from going early morning.
Find out when your specific store does mark-downs - Usually 3pm and 5pm.
Note, some grocers do their mark-downs first thing in the morning (opening time)
If your grocer is open late, try between 9pm and midnight for mark downs.
** Fruit is cheapest at the end of the week, so go Friday and Saturday.
While I can't verify this, some people say Wednesday mornings are good days for mark-downs as some grocers do mark-downs on Wed in preparation for the end of the week shipments.
Another day known to be the cheapest is Sunday evening.
The best advice I would give here, would be to get friendly with someone at your local grocer and find out when they do most of their mark-downs.
More grocery shopping saving tips:
Beware of marketing strategies - Super markets know how to catch your attention to try to sell you.
Related Coverage
Money Saving Tips For Online Grocery Shopping

There are many ways to save money when you are getting your groceries from an online grocery store. You will be able to save more money by shopping online and following a few tips that will come in handy. Shopping at online grocery stores will enable you the convenience that you require while allowing you more time to do other things in your life that was formerly taken up with grocery shopping. Five Big Tips to Save More on Grocery Shopping

Grocery shopping can be fun if you use these helpful hints and ideas to lighten your load but not your wallet. Clean the refrigerator out before shopping. Look closely at the food you already have. If the fresh produce is past using in a salad, plan a meal using it in a cooking recipe. Ninety-five percent of wilted produce can be used in stock, stews or a sauce. Don't waste it, use it! 10 Tips For Saving Money When Food Shopping

MAKE a grocery list and stick to it. This will decrease your chances of purchasing more than what is needed. Saving Money on Groceries Using Coupons

No matter how frugal you may be, you are always going to have to buy groceries- we just can't live without food! Unless you are a farmer and raise all of your own livestock and grow your own fruits and veggies, you are going to have to buy some food.If you are aware of these ploys, you can avoid them.
Check products below or above eye-level - This is one of those marketing strategies mentioned above. Manufacturers pay grocers for premium eye-level product placing. You are the one that ends up paying for this premium placing!
Make a list and stick to it. - If you go out with a list and only buy what's on the list you will spend less than if you go to the store and buy what you think you need for the week.
Store and Plain Brands - Try plain brands or store brands, they are almost always as good as more expensive labelled brands and are even better sometimes.
Why pay for pretty advertising on your cat food tin when the plain brand stuff is half the price?
Coupons, Rebates, and Frequent Shopper Programs - I'm not a coupon user and probably never will be but it's a fact that added up over a year using these can end up saving you hundreds of dollars. A recent study showed on average a 10% saving over a year.
Check Sunday papers, contact manufacturers directly and ask them if they have coupons they could send you and ask to be placed on their mailing list, check store displays as they often have more coupons and go online where you can often find printable coupons not available by conventional means.
Trying shopping like a European - If money is really tight, a technique mentioned to us by a subscriber is this: Shop like a European - This means you buy the stuff you need for dinner each day. This helps in 2 ways: One, you don't have to spend one big lump sum of $$$ for a week or two's worth of groceries.
Two, it lets you decide your meal based on what is on special. Some people (especially singles or couples with no children find this can be very economical).
Eat differently - Dinner doesn't have to be steak with vegetables. There is nothing wrong with a simple (and CHEAP) pasta dish or a sandwich for dinner! You may not be used to it but another cheap way of eating is with stews or curries. It doesn't matter what goes into it, call it 'Gumbo'! The beauty of it is you can let the price of ingredients dictate what goes into it. Buy all the cheapest stuff and throw it all together in a huge pot, cook for an hour or two and portion it out for the next few days. Do you often make soup? If you want to save money, soup is great! Not only do you eat less if you start out with soup first, soup is cheap!
Ethnic Grocers - Try Asian or Indian grocers! You will often find many items cheaper in these stores but you may find a whole new range of ideas which are cheaper than the way you do it now!
Don't shop on an empty stomach - Science boffins have proved that if you go shopping when you are hungry you spend more money than if you go after a meal. The reason, you're subconsciously buying more because your hunger is making you feel you need more.
*** Shop at markets at the end of the trading day. If you can, shop at farmer's markets for the best quality and the cheapest price. In my area (West End in Australia's Queensland) there is a small market with a huge range of foods and if we arrive just when the stall owners are just about to pack up you wouldn't believe how cheap we get our groceries. Doing this we get our groceries done 4 times as cheap as if we did all our shopping at Woolworths! Example; ONE dollar for a big bunch of bananas that would be $6 at a big-name grocery store.
We hope this has given you a few ideas and will save you money.