I'm new to this forum, so please excuse me for posting some thoughts on a topic that may have been discussed at length in past:
Offering advice to the general public often requires simplifying the message, and this is difficult when very little is known about how the disease is actually transmitted. Essentially all studies of SARS viruses transmission have focused on how the virus gets from an infected person into the environment. The other essential aspect of transmission is getting from the environment into the susceptible host.
The WHO and CDC guidelines have emphasized hand washing and cleaning potentially-contaminated surfaces as preventive measures. However, none of the references cited in the WHO's scientific brief on COVID-19 transmission provide any direct data that support the idea that people become infected through contact with contaminated surfaces. It's also unclear how SARS2 (COVID-19) viruses on one's hands would end up where they can invade susceptible cells and cause infection. SARS viruses infect by attaching to ACE2 sites on the surface of certain types of cell. In humans these cells are found deep in the lungs, as well as in the walls of blood vessels and the lining the upper and lower intestines. Cells with surface ACE2 receptors do not occur in the lining of the nose, mouth or throat, so it's not evident how touching there would cause infection. A couple of recent preliminary reports have described finding ACE2-positive cells in the conjunctiva, so touching your eyes could possibly result in infection.
This topic is difficult to study, for one cannot ethically do the kind of human experiment that would be most informative. Nevertheless, analyses of point-source outbreaks has provided some helpful insights, which Erin's blog has so nicely described. In addition, contact-tracing will identify persons who did, and did not, become infected, and careful questioning of them about their activities and sanitary practices could provide helpful information. Despite the many uncertainties, I still think that data from studies of COVID-19 outbreaks point to inhalation of aerosolized virus as the most important route of infection.