Regularly defrosting your freezer can massively improve its efficiency. The ice that builds up becomes an insulator, reducing the effectiveness of the freezing process. Also make sure you use the whole of your freezer, rather than leaving it only half-full.

Conversely, make sure you leave space in your fridge. The fridge needs space so that cold air can circulate, allowing the fridge to operate efficiently. It’s also worth vacuuming the cooling coils of your fridge on a regular basis, otherwise the fridge needs to work harder than it needs to (using more energy).