Keep your appliances maintained to make sure they perform properly. For example defrost the freezer regularly, check the seals, bleed your radiators, descale the kettle,etc.
Keep the doors of the fridge and freezer opened for the strictly necessary amount of time and don't put hot/warm food in them.
Use pressure-cookers, steamers and microwaves, which use less energy than a conventional oven.
Fill up your washing machine before turning it on, and make sure the lowest setting is selected for the wash.