Remove everything and clean the fridge interior thoroughly. If it's heavily soiled, place highly perishable items in a cooler or separate refrigerator.
Toss any foods that have expired. Check expiration dates. Remember: leftovers only have a shelf life of about 3 days.
Sort foods into groups: milk/cream/bottled juice, produce, cheese & deli meats, condiments, etc.
Create zones for the food groupings. The bottom of the fridge is the coldest, best for raw meats and leftovers. Don't store milk on the door, it's too warm there.
Use clear, stackable bins to corral food groupings and label them to ensure foods get put back in their proper place.