One frugal tip that seems second nature to me because I have been doing it for about three years now--plan your shopping trip to get the best deals. However I still run into people all the time who do not do this.
One example--as a teacher in a preschool that encourages family involvement I build relationships with my families so that by this time of year we are visiting at conferences/home visits like old friends. One mom mentioned that she would like to serve more fresh fruits and vegetables, but they are so expensive. They certainly can be, but as we continued the conversation I discovered that she did her grocery shopping at Walmart and she had just bought a big bag of apples there that were just on sale at Fareway the week before.
I always keep a decent amount of apples in our fridge, but I am not terribly picky about the variety of apple that we get. I choose the variety that is on sale and there seems to be one on sale every week. I also check the ads in our weekly Advertiser, compare them to Sara's match-ups at Learning the Frugal Life (she has these up by Wednesday each week), and plan my trip accordingly. I always have fresh produce on my list, but the actual items vary with the deals that are going on. I buy carrots when they are on sale. I buy lettuce when it is on sale and so on.
I stock up on items that will keep when I find them on sale and especially if I can stack advertised sales with coupons. Peanut butter and ketchup are hot items right now and we seem to go through a lot of these. I would rather buy them now for a fraction of the price, than buy them for full price later. Hot Coupon World has a list of sales cycles that helps new deal hunters to know when it is the best time to shop for various items. They also have a coupon database where you can search for available coupons for the items on your list.
Don't be brand loyal. Know your sales cycles. Plan your trip to purchase items on sale. Stack sales and coupons when possible. Stock up on non-perishables when you get a deal. Make one trip to the store per week to save on gas. Pinch those pennies and make them count.