12. Never touch your face without washing your hands first

This goes back a long way to the medical origins of germ theory, that there are physical things–call them germs–that are the cause of diseases and not some ethereal ether or vapor or miasma that skips around the town, village, hut, household and makes you ill. So, a very practical, simple, effective, well-tolerated and cheap method is to wash and physically remove these germs from your hands so they cannot get into your body through the mouth or nose and cause you to become ill. 

The eyes rarely are an entry point of illness due to a very powerful anti-germ chemical in the liquid surrounding the front of the eye, the tears. So, if your hands are relatively germ-free then you cannot transfer a sufficient number of germs to a point of entry and allow illness to gain upon you. Alternatively, always wearing an effective mask that covers the nose and mouth would work well. We will leave it up to you: belt, suspenders, belt and suspenders.