Food is one of the biggest costs a family must face and one of the toughest to cut back. Unlike a regular bill that comes once a month in the mail, grocery costs change with each trip to the market.

Many people start their grocery trips with this question: "What do I want to eat this week?"

"If you do that, you've already lost," says Jeffrey Strain, creator of the "Eating Well on $1 a Day" blog at GroceryCouponGuide.com.

Instead of deciding what you want to eat and buying groceries accordingly, Strain says making one change will save you well over 50 percent.

"Decide your meals on what you already have and buy the stuff that is super-discounted, and you're going to save a ton of money," says Strain.

While you may not get your food costs down to $1 per day like Strain has, these six tips can help you save money on groceries.