1) When you drink bottled water, save the bottles and fill them up with tap water. Put them in the freezer. They displace air and hold the cold better, saving energy in the freezer. Plus they can be used for drinking water in an emergency. If the freezer gets full, just take them out and set them aside, and put them back in later.
2) Unplug unused appliances. Many of them use electricity even when powered off. There are other fancy devices you can buy to optimize further without leaving them unplugged all the time. See
3) If it takes a long time for the water in your shower to get hot, save the cold water in a bucket. Use it to flush the toilet(flush the toilet then pour the bucket in the tank).