Stick the kettle on - fill the kettle with what you need by measuring the water with your cup. The kettle is also more efficient than boiling water on the hob.
Toast! - Using a toaster is far quicker and efficient than using the grill.
Heat up quicker - heat food quicker by using your microwave, slow or pressure cooker. All are more efficient than using your oven.
Keep the lid on it - try putting a lid on your pan, this will heat the contents quicker and save energy. Use a ring on the hob that matches your pan, if the ring is too small and the pan is too big this will waste energy. Or try putting more than one thing in a pan.