Protecting your body also includes monitoring what you put in your body; not just in regards to food but with toxins, drugs, and alcohol. Recreational drugs can have a detrimental effect on your organs, blood vessels, brain etc. Too much alcohol consumption can be detrimental to one's liver and digestive system. Refraining from smoking is also a must to protect your health.
This is such a broad question as to be open to many different lines of answers
Protecting your body could start with buckling your seatbelt when in a vehicle, wearing a helmet when riding a bike or motorcycle, using elbow and kneepads when skateboarding, and so forth.
Protecting your body could include using sunscreen, protection from bug bites, and deterrents to the oils of poison ivy. Protecting your body means being careful when using potentially dangerous equipment, being aware of falls when hiking, watching out for low clearance when exploring caves.
Protecting your body includes eating safe foods that have been properly prepared in healthy conditions. Drinking enough water and other fluids protects your body.
The best way to protect your body's health would be to eliminate stress, or at least significantly reduce stress. Also, supply your body nutrience from whole food fruit and vegetable sources (preferably locally grown and organic).