Don't buy more fresh than you can use before it goes bad. Check the refrigerator and deep freeze before shopping. Use foods that are in season when you can, they should be cheaper. Don't waste the leftovers. Learn how to be a creative cook.
Experience does wonders.
This is a good reason to plan your menus in advance. Read the labels and compare store brand items to famous brands. They usually cost less and are just as good. Start from scratch rather than prepared freezer or packaged items. Get used to eating meals at home and make it a special family time rather than eating out.