
Putting a house brick in the cistern of your toilet will help save water as not so much is used when it refills itself after flushing. And getting into the habit of turning the tap off whilst brushing your teeth will save loads of water too, just turn it on when you need to rinse your brush.
Keep a water butt in the garden so as it will fill up with rain water which you can then use in the summer for watering Plants.
Start a compost heap. This really reduces the amount of household waste you would normally put in your bin plus you'll have super nutient rich soil that your Plants will just love you for. You can compost all veggie peelings, tea bags, ground coffee, in fact everything except meat, bones, dairy, oils and peanut butter.