Preserving the earth's environment is all about keeping the rate of our usage of the earth's resources slower than the rate at which the earth can regenerate the resources, the earth's resources will be available to us indefinitely and our subsequent generations can enjoy the earth as much as we do.
Conserving water saves you money! Not only will your water bill go down, but as you heat less water, your gas or energy bill will also decline. If your whole community conserves, you will also pay less fees for water-related services. Water conserving communities will not need to pay as much to develop new supplies and expand or upgrade water and wastewater infrastructure.
Refuse, Reuse, Recycle: don't acquire what you don't need. When you do acquire stuff, make sure they are reusable or at least recyclable.
Reuse: cloth bags for groceries instead of paper/plastic.
Recycle: donate old furniture, computers, clothes, books instead of trashing them.
Use recycled material wherever you can (and products thereof).
Avoid waste (unnecessary expenditure) of time, energy, money, material, resources. This is a good thing to do in general. Of course, the relative pros and cons need to be considered on a case by case basis. (Example: walking to work is not an excuse to come late to work everyday.)
Encourage businesses that behave responsibly. Discourage those that don't.
Use common sense:
Don't acquire stuff just so that they can later be recycled. Example: recycling plastic water bottles, paper/plastic/thermocole cups is good. Even better is to reuse a bottle or a cup (say, to refill from a water fountain).
Avoid being taken advantage of by people/companies that try to make a quick buck in the name of saving the environment. Examples: dubious 'organic' labeled products, organic products sold at an exorbitant price, 'alternative' anything that is sold at a premium that doesn't make sense, etc.