Last month, I enjoyed shopping with a TV producer at a Giant Eagle grocery store in Pittsburgh to demonstrate coupon saving strategies. She asked me something I had never been questioned before about, "What are the top mistakes shoppers make that cause them to spend too much money?"

I gave quite a bit of thought to her question, and came up with my idea of what the top mistakes are:

1. Not having a plan. Common sense suggests that shoppers who plan and stick to their shopping lists spend less money than shoppers who go to the store with only a vague idea of what they need to buy.

The shopper without a plan is much more likely to buy items on impulse, to pay higher prices than necessary because they aren't aware of sale items, and to come back to the store the next day because they didn't remember everything they needed during their unplanned trip.

Conversely, the shopper with a plan would have their meals planned around what the best sale bargains were that week, they would have thought through everything they needed to last at least a full week to avoid frequent (and expensive) trips, and they may even have coupons to match sale items. The shopper with a plan would most likely spend 50 percent less overall than the shopper without a plan. The 30 minutes required to make a good plan pays off.

Even if you find yourself in the store parking lot without a plan, you can stop and jot down your best attempt at a shopping list, and grab the store sales flyer as you go in the store. Quickly scan the front and back pages of the ad to make sure you get any super-bargains. Shop quickly to avoid spending more time and money than necessary!

2. Not using grocery coupons. Over the years I have heard countless reasons why people choose not to use coupons (I am too busy, coupon food is unhealthy, there are never coupons for items I buy, etc). I also know plenty of busy shoppers with healthy eating habits who save hundreds of dollars a year with coupons.

At the very least, shoppers can flip through the weekly coupon circular to find coupons on items they like, even if the only "coupon items" they use are deodorant and toothpaste. Most people use those items. Coupons are free money when shoppers use them!

3. Being too brand loyal. Most shoppers buy the same products repeatedly, whether they actually prefer the brand or are simply buy the product out of habit. However, comparable brands may be at a rock-bottom price or even free with a coupon if they are featured sale items.

At that point, it's worth it to try a new brand. If you must have the same brand for a particular item based on a true preference, then watch for sales and stock up when it hits its lowest price.

4. Using coupons too soon. Most coupon shoppers cut out a few coupons from the circulars and use them that week. However, your best strategy is to wait until your coupon items go on sale to use your coupon. If you track prices for your most common items you will discover their prices have fairly predictable cycles.

Therefore, if you know your favorite salad dressing or cereal is a common "buy one, get one free" item at your store, wait until it hits that low price before using your coupon, which your store may even double. The average coupon expires two and a half months after it is issued, so you can wait a few weeks before using it, if necessary, to pay the lowest price possible for your favorite items.

Those are my answers, and if you have any additional answers, please send me a message. I'd appreciate hearing your ideas!

Stephanie Nelson shares her savings tips as a regular contributor on ABC News' "Good Morning America." You can find more of her savings tips in her book "The Greatest Secrets of the Coupon Mom" and on her website at www.couponmom.com. She can be reached at shoppingmom@unitedmedia.com.