Switch off anything that uses electricity. Stick to a routine of shutting off as many electrical appliances as possible when you leave a room. If it will be at least 36 hours before you use it again, unplug it. Even when an appliance is off, it can still suck up juice. Just imagine. You will save hundreds of dollars and you could donate the money to a charity in need or buy yourself something nice.
Check your faucets and any other appliance that uses water straight from your source. If your faucets drip, get them fixed, or at least put a container under the drip in the meantime and use the water. To check your toilets, put a few drops of food colouring (go for a strong colour) in the tank, not the bowl. Wait about ten minutes without flushing. If you see the dye in the bowl, repair your toilet.
Turn off the water when you're not using it. As Ellen Degeneres says, "Turn off the water while ." Why is the water running for so long? There is no point, is there? It is okay if you forget a few times, but if you forget a lot, put a little sticky note on the wall in front of the sink, with the reminder, "Turn off the faucet. Don't waste water!" This goes for shaving, washing dishes, and even taking a shower.
Use rechargeable batteries instead of disposable batteries. Batteries not only take up landfill space (they can't be incinerated), they can leak acid into the Earth. Even then, only use the appliance when you must. If you have the choice, plug in the device instead of using batteries.
Clean or replace air filters on your air conditioning unit at least once a month.
Use a ceramic coffee mug instead of a disposable cup