We are human, made of flesh and blood and it is impossible that we shall have no illness. But, if we are to pay careful attention to our sleep, food, exercise, illness will not fall upon us.
First of all, we must build ourselves a body of strength to resist any illness which may attack us at any time. But, to build a strong body is not easy, it may take years to do so. That is that we must have ample sleep, balanced food, adequate exercise and a peaceful mind. Besides, we must not have night life, and forbid drinking alcohol and smoking.
If you can do above, small illness, such as cold and fever or any kind of stomach problems, headache, etc. will never fall upon you.
The only thing you have to be beware is accident. But, as far as accident is concerned, we have no way to prevent from happening. We may meet earthquake, land slide, flood and nature disaster or we may have plane, railway, steamer and car accident, all of which we do not know when will happen to us. We can only leave to our destiny and at the mercy of God.
What we can do is take care of our own body, not letting disease inflict upon us. Therefore, we should, every day, have enough sleep, eat balanced food, and take adequate exercise. As long as we take those precautions, illness will not visit us basically.