You should dress appropriately when you are outside in accordance with the weather. This mostly applies to the winter season. Make sure you wear something warm on your head, and dress in layers of clothing that will keep you warm and insulate you from the cold.
Make it a point to exercise daily. Engage in cardiovascular exercise and weight training. This will help keep you fit and healthy and drastically drop the amount of times you need to visit the doctors.
Quit unhealthy habits. You should definitely eliminate habits like smoking, drinking, or staying up very late every night. These habits will lead to health problems in the future.
Supplement your diet with vitamins. A good multi vitamin will do the trick and others include Vitamin C, Omega 3 Fatty Acids, and Vitamin E.
Don't engage in high risk activities if you can help it. By being cautious and safe as well as not doing stupid things, you will cut your hospitals visits down as well.