Transparency. Transparency means being able to see what people are doing and who they are doing it with. Technology is really helpful in helping people see what is really going on.
Laws that support transparency help. Laws that suppress the availability of information hurt. A cultural attitude that supports honesty and does not support corruption helps. A perception of fairness is important.
Most people are corrupt because they think the system in their culture isn’t fair, and so they should do what they can get away with because everyone else is doing it, and if they don’t get over one someone else, someone else will get over on them.
Law, culture and communication support transparency, which fights corruption. Secrecy is corruption’s friend.