How can i have very strong bones and body, to be very immune to any type of disease and also to external damages (e.g. falling down, ...)?

Good diet/exercise.: Being healthy through proper diet and exercise protects from disease and sometimes injury. Avoiding tobacco, alcohol and recreational drug use also helps. Getting enough sleep is also important. Plenty of fruits and veggies, low fat, helps. Avoid high protein diets. Weightlifting, flexibility routines, and balance training (yoga, for instance) all help prevent falls, injuries. Helmets! Seat belts!