Cooling and Heating

Reduce your need for cooling and heating devices
Close the doors to unused rooms to reduce the area you need to cool or heat.

Keep curtains and outside window shades closed to reduce the amount of energy needed to maintain a consistent temperature inside.

Seal drafts around doors and windows.  Hardware stores sell inexpensive strips which attach to doors and windows to stop drafts.

Rather than heat your bedroom, add another blanket to your bed or use an electric blanket, wheat bag or hot water bottle.

Look after your cooling and heating systems
Clean your air conditioner or cooler so it doesn't use as much energy. Turn off your cooling or heating overnight and when you're not home.  In the summer set your room temperature to between 23 to 26 degrees C.  In winter heat the rooms you are using to between 18 to 21 degrees C.  Lowering the setting in summer and raising it in winter, even by one degree, will considerably increase your electricity bill. 

Insulation
Consider installing insulation in your house.  You will save money on heating / cooling bills and will be much more comfortable.

The temperature control problem in most houses is not heating or cooling the house at all – it is retaining that comfortable temperature.  Heat will eventually leave but will do so much quicker when there is nothing stopping it from leaving via uninsulated walls, ceilings, windows or floors.

Conversely in summer, the outside heat gets into the house through the uninsulated walls ceilings windows and floors and heats up the house to a high and uncomfortable temperature.  When insulating, it is a good choice to also insulate all hot water pipes so as not to unnecessarily lose heat for baths and showers.  Insulation is sensible and cheap.