#1 way to prevent illness is handwashing. This is a scientific fact that has been proven.
Wash your hands.
Zinc works, but not Cold-Eeze. See this: https://chrismasterjohnphd.com/2016...fights-colds-youre-probably-using-wrong-kind/
Yes, most people don't realize how often they touch their faces throughout the day. That's how germs get in. Even if you wash your hands often, you can still pick up germs in between washings. Try to remember not to touch your nose, eyes and mouth, and use a paper towel to turn off the faucet and open the door in the rest room.Don't touch your eyes/nose/mouth when you've been touching door handles, handrails at the attractions, etc.
Get enough sleep.