Here's a seemingly basic yet frequently overlooked tip for using coupons..
Read the coupon and buy small!
What this means, in a nutshell - is there any size or product restrictions on the item that your coupon is good for? Reason being because more times than not... it is almost always better to buy the smaller size or quantity with the coupon to get the best deal. Always keep a calculator handy!
Ruffles Potato Chips
Coupon for $.50 off one (restriction: 7 oz or larger)
There's a Regular 9 oz bag on special sale for $1.99 and a Family Size 13 oz bag normally priced at $3.79. Instinct might tell you to buy the significantly larger bag (which only has 4 oz more inside) and pay only $3.29 HOWEVER if you look at the price per ounce you'll see that the smaller bag is the better deal.
9 oz bag (price w/coupon) $1.49 or $.165 per ounce.
13 oz bag (price w/coupon) $3.29 or $.253 per ounce.
Always have your calculator handy... it'll pay off at the cash register!