Firstly, get your shots. Get vaccinated annually, especially against flu. But if you travel internationally, especially to the tropics and to poorer countries with sanitation issues, get yellow fever, dengue, and malaria vaccinations as well. Arm yourself with Cipro. You may not have to take it, but it's good to have.
As to actually flying...use hand sanitizer frequently, especially after trips to the lav. Bring disinfectant wipes and wipe down the armrests, tray table, and vent ring. And don't forget the IFE controls as well. Do it at the start of the flight.