Eat right! Make sure you get your daily dose of fruits and veggies. Take your vitamins and bump up your vitamin C. Get plenty of exercise because exercise helps build your immune system. Walk for at least one hour a day, go for a swim, take the stairs instead of the elevator, etc.
Wash your hands often. If you can't wash them, keep a bottle of antibacterial stuff around. Get lots of fresh air. Open windows whenever possible. Get plenty of rest. Try to eliminate as much stress from your life as you can.
OR .... You can take the doctor's office approach. Think about it, when you go for a shot, what do they do first? Clean your arm with alcohol. Why? Because alcohol kills germs.
So... I walk to the liquor store (exercise), I put lime in my Corona (fruit), celery in my Bloody Mary (veggies), drink on the bar patio (fresh air), get drunk, tell jokes, and laugh (eliminate stress) and then pass out (rest). The way I see it, if you keep your alcohol levels up, flu germs can't get you!
Image Credit: Matanuska-Susitna Borough