By being aware and responsible for your own Body. What you put into your Body, where you live(chemicals, fertilizers other toxins), association w/toxic people around you. Learning about nutrition and not becoming O/C about anything.
Be kind to your Body and it will respond in kind.

Being your own body and mind's best friend is key, as is educating yourself about what toxins are out there, including every aspect of one's day, and trying to figure out how to protect oneself. There are many toxins in the air that we breathe, the food that we eat, containers for the food that we eat, how food is processed, the chemicals we put on our bodies, and on and on. Some ideas are:
Keep toxic drugs out of one's system, and don't ingest others' carcinogens.
Prepare food "from scratch" as much as possible, and don't worry about time.
Processed foods lack vitamins, antioxidants, and many other health giving substances.
Try and avoid processed foods, high fat, high salt, and high sugar content.
For ourselves and the environment, avoid plastic bags as much as possible. Use paper bags.
Or use bags that can be composted as they are made of vegetable substances.
Steam fresh food as much as possible, and emphasize fresh vegetables and fruits.
Be aware of all the toxins there can be in food, such as wax on fruits, and toxins in fish.
Reduce stress and maintain a healthy weight, to help the immune system function.
Ask doctors questions about what is healthy. Read food labels. Stay away from toxic dumps and contaminated zones. Yes, balance is important. And don't believe the advertisements!