Only fill the kettle with the minimum amount of water. Never boil more water than you need. If the kettle is on for only 2 minutes per boil then you emit about 100kg of CO2 every year. If it's on for 4 minutes per boil then you emit 200kg of CO2. (maths: 2kW x 365 days per year x (2minutes / 60) hours x 10 times per day x 0.43 kg of CO2 per kiloWatt hour = 105 kg of CO2 per year)
boil water in the microwave instead of the stove top.
Turn the cooker down as low as you can. For example, if you're boiling an egg then put the gas / hob on full until the water boils, and then reduce the heat. The water will continue to boil but you'll be using less energy.
Next time you need to replace a light bulb, use a fluorescent lamp instead of an incandescent lamp. A 20 watt fluorescent lamp gives as much light as a 60 watt incandescent lamp — an incandescent lamp converts only 10% of its power into light; most of the rest gets converted into heat. (But because of this, switching to a fluorescent lamp may make the room feel colder.)
Reduce the number of lamps in a room. One 60 watt lamp may provide sufficient light instead of two 40 watt lamps.
Consider solar power. But do the homework in terms of cost and benefit before making a decision.
Use Energy Star-compliant and similarly energy-efficient appliances.
Use rechargeable batteries. This reduces the number of dead batteries to be trashed, and hence the amount of hazardous chemicals in landfills.
If your home computer doesn't need to be 'always on' (e.g., it is not used for work), consider consolidating your computer usage to only a few hours every day. Turn the computer off the rest of the day.
Use draft instead of air conditioning during hot days.
Plant a tree(s) so shadow will reduce heat during hot days.
In the winter, set your thermostat at 68 degrees in the daytime and 55 degrees at night. In the summer, keep it at 78.
Showering uses up 40% less water than a bath.
Install low-flow shower heads and faucet aerators.
Wash full loads in your dishwasher and use short cycles for all but the dirtiest dishes.
Set the appropriate water level for different size loads in your clothes washer, wash in cold water when practical, and always rinse in cold.
Don't use dryer to dry you clothes after washing. Let them dry themselves on hangers or rope in natural way.
Wrap your water heater in a water heater blanket, especially if it's located in an unheated part of the house. This prevents heat loss through radiation.
Opt-out from unwanted mailings: credit card offers, free newspapers, catalogs, advertisement, etc.
Use Internet for latest news or library for newspaper/magazine articles.
Bring reusable bags with you when you need to visit stores.