Here are a few of my suggestions...
Wash hands often - especially when you've been "out in public" (church, grocery shopping, etc). I prefer just plain old soap and water, but I will also rinse my hands with cold water if nothing else is available. I heard a Dr. on tv talking about cold/flu prevention and he said that even rinsing your hands with cold water would help wash off cold virus germs. And I keep a thingee of hand sanitizer in my car for emergencies.
Gargle and spray - twice a day! - Go to the Dollar Store and get the store brand of Listerine (or you can use just plain 'ol salt water) and gargle in the morning and at night. Also get some saline nasal spray and spray your nasal passages twice a day - morning and night. The nasal and throat passages are where the cold/flu germs collect and are stored, so keeping these passages flushed often is a big help in preventing the flu/cold.
Drink lots of water - really. This helps to flush the toxins out of your body.
And I am a big believer in vitamin D3. It's an easy thing to do.
Stay away from people you know are sick - unless they're your kids! (well, that one's a no-brainer!
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I haven't taken a flu shot in years and I also haven't gotten the flu in as many years. The last time I, along with my son, got the flu shot, we also got the flu.