"Humor Me" Simplicity Tip #7 is clean out the fridge weekly for a month.
You and your family interact with your refrigerator several times a day, and like any frequently used space, it requires frequent maintenance. But I'm willing to bet it doesn't get it. Try cleaning it out once a week for a month and see how you like it. Ideally, do it the evening before the trash guys come, so you don't have a trash can full of old food in your kitchen overnight. Once you begin getting used to keeping items moving out of the fridge and into the trash on a regular basis, you'll be more aware of what's old, and throw it out on the spot, rather than just leaving it sit there growing green hair until clean-out day.