EXERCISE CONTROL. Practice "WASTE NOT". Adults check each other. Children learn from adults. Ricardo is right. Exceeding controlled cost means forgoing something.... like no watching TV for 3 days or no going out for restaurant food the following month and such litle self punishments will bring order and discipline.
In my apartment, we are three 20-somethings with incredibly busy lives, so it's not always that easy to devote too much time, but we do try our best.
For starters, we recycle. Since we have started doing so, it has made us more conscious of our actions. We ALWAYS turn off all electronics and even unplug those electricity sucking items (XBox, TV, etc.) It's also really important for us to only use what we NEED and not necessarily what we want. We wash and re-use glass/plastic jars and containers for other purposes. We also have a filtered water jug in our fridge that we drink out of, instead of plastic bottles.