AC On
There’s very little you can do to prevent germs in the airplane cabin from getting all over you. If someone coughs 50 rows behind you, it’ll only take a matter of minutes their germs reach your seat. Hopefully, your immune system is in tip-top shape.
To help keep germs away, you should turn your AC on at full blast. The air will work as somewhat of a barrier to blow germs and airborne contaminants away from you. It sounds primitive, and it’s certainly not better than wearing a mask, but every little bit helps. Catching a bug on your flight is never fun.