When you clip your coupons, you will notice that some say, "Manufacturer's Coupons" (the vast majority) and some say "Store Coupon" or will say, "Target Coupon" or "Food Lion Coupon" or something to that affect. When you have a manufacturer's coupon and a store coupon for the same item, you can use both coupons for that item, thereby creating a situation known as stacking the coupons (and saving twice as much).
I'll give you an example. I regularly get coupons in the fliers for use at Target for $3.00 off Pampers. I also have manufacturers coupons for Pampers for $1.50-$2.00 off. When I got to Target to buy Pampers (they are on sale this week, BTW), I will use both coupons, effectively getting $5 off my coupons. You can ALSO do one more trick with this as well. I frequently get a coupon from Pampers saying, "Get a free box of wipes when you buy one box of Pampers". In this situation, I will use ALL THREE coupons and get $5 off AND a free box of Pampers.
With coupons, you have to learn to think outside the box and to know the store policies on coupons. If you don't know your store's policy you can either 1) go to the store's website, 2) ask the manager or customer service desk on your way in, 3) leave a comment and if I know I will share that with you.