My mother has had problems with her lungs for years. While never a smoker, she developed a nasty infection that left her lungs very vulnerable to infection.
I am not as fanatic about infection prevention as she is, but here are a few things we both do in order to protect ourselves against infection. She does these year-round, I really only do it in flu season.
If you are over 60, ask your doctor about getting the pnuemococcal pneumonia vaccine. It won't protect you from the flu, it will protect you against flu-related pneumonia.
Wash your hands. Before you eat, after you eat, after you have handled money. Wash your hands, rubbing briskly, sing the happy birthday song twice. (This is great way to get kids to wash their hands long enough.)
There are antibacterial gels that you can get to use and those are great for on the run, but nothing beats a good old soap and water washing.
My mom and I carry the antibacterial wipes and wipe down shopping cart handles as well as wiping our hands. My mom sometimes uses them to actually open a public door with. Never leave a public bathroom and actually touch the door handle/knob with a bare hand (the last person to leave may not have washed up) use a paper towel or an antibacterial wipe.
I open doors with my LEFT hand as I am right handed and if I'm going to stick a finger in my eye or nose subconsciously, I'm going to use my dominant right hand.
Don't be polite. If someone near you is coughing and hacking their lungs out, move, get away.
Eat right, get lots of sleep and exercise.
Thor sez: And make sure no swines have been using your toof-brushie!