Like for diarrhoea germs, the top preventive is hand washing especially if you are keeping stuff clean for a family or for an institution like a restaurant, school, or old peoples home.
Normal good domestic cleaning of kitchen and bathroom surfaces is also quite important.
Unlike for instance some disease germs, the coronavirus, like many other viruses, is also spread by invisible droplets from coughing or sneezing or even breathing. If you want to be very very safe, stay away from enclosed spaces with other people in them.
General natural immunity is a good preventive. Get enough rest and sleep and some exercise as suits you especially in open air. Drink enough fluids. Don't smoke. Eat nourishing food.