Over the course of a year your fridge and/or freezer can be one of the most energy intensive items in your home and may add over €100/year to your electricity bills. Try to only open the door to your fridge when you need to and close it as soon as your finished taking out what you need. Don't open the door unless you are removing food (food browsing in the fridge is one of hardest habits to break).
Operation: If your freezer is not a frost free model, make sure you regularly defrost the freezer if ice builds up. Regularly clean the coils behind appliances if they become dusty as this reduces the efficiency of the heat pump. Set temperatures for freezers to -16 to -18 Degree C and fridges to 2 to 4 Degree C.
Longer term, look to replace your fridge and/or freezer with A rated or better yet A+++(triple A) rated products.